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# System prepended metadata

title: Simple Fish Keeping Guide

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# Simple (Freshwater) Fish Keeping Guide
Before I continue, I think it's worth noting:
- I have less than a month of experience keeping fish in a tank (~20 days). They are currently looking very lively and healthy.
- I spent possibly 25+ hours passively learning about fish keeping, mostly ever since I acquired my fish.
- I am keeping 2 juvenile [Prussian carp](https://en.wikipedia.org/wiki/Prussian_carp) I caught from a small, random pond in the wild. Prussian carp are in the same genus as goldfish and essentially behave the same way. Thus, my direct experience extends to goldfish only. These fish are hardy and easy to keep.
- I am keeping them in a nano-tank (7L / 1.8 gal) bought from German Amazon that came with all needed equipment. The filter and powerhead create a strong current.
- Some of this text is contrarian.


## Aquarium Cycling
"Cycling" is the most important component of understanding aquariums. It refers to the process of growing colonies of (beneficial) bacteria in the tank to complete the nitrogen cycle.

Fish and food waste produce ammonia, which is toxic to fish. Ammonia is converted to nitrite by the bacteria (and plants, but [don't get plants](https://aquariumscience.org/index.php/1-1-10-plants-and-the-new-hobbyist/) as a beginner). Then, other types of bacteria convert nitrite to nitrate. The cycle is complete.

Now, it just so happens that nitrate is _also_ toxic to fish, and there's no way to get rid of it except for doing water changes or having plants. This is why you have to actively maintain a fish tank. A good rule of thumb is to change a third of the water volume every week. You can definitely slack off on that but you will _probably_ be harming the fish long-term (idk how negligible the difference is). Probably not going to be an issue unless chronic.

> Note: There is no universal formula or rule for water changes or pretty much anything else. Water changes depend on waste, aeration, total volume, and so on. Cherry shrimp produce so little bioload that you can leave them for months without water change in a larger bucket with a plant. You can also create a completely self-sufficient aquarium that you will never have to do water changes in, but it's **not** going to be aesthetically interesting and won't support a lot of fish. If you want to be precise, measure parameters such as nitrate and ammonia by ordering test kits (for nitrate: keep below 80 ppm (the high end); the lower, the better, but sometimes not worth investing too much energy into), though they're likely not going to be necessary. A bit of common sense is fine too, and personal judgment.

It also just so happens that bacteria can be harmful for fish, too. You don't want too many bacteria: the fish's immune system will expend resources fighting them and be more vulnerable to all pathogens, and they will get sick.

So, what you need to be looking out for is to grow colonies of bacteria that can complete the nitrogen cycle, but you don't want bacteria to totally take over the tank.

> Note: One of the best signs of a healthy tank is [crystal clear water](https://aquariumscience.org/index.php/6-4-crystal-clear-water/). Win-win. When people have dirty tanks, they're doing something wrong. See [here](https://hackmd.io/_uploads/r1bdLZ5XJg.png).


>Note: Normally, bacterial colonies are mostly found on surfaces (glass, substrate, filter media, tank decoration). Water changes will not intervene in their development.

The issue with a new tank is that is has _no_ sizable colonies of bacteria, which take time to grow, so you may end up with a build-up of too much ammonia before the equilibrium is reached.

This is why people recommend you be a little careful with your new tank. You can either let it run without any fish for a some time while dropping small pieces of food every day or put in some (ideally smaller) fish (who ideally produce little waste) and feed lightly. It takes a few weeks (let's say a month) for the new fish tank to cycle.

If we take the fishless method, the small pieces of food will serve to feed the bacteria. It is common to see products like "bacteria in a bottle" in stores that are purported to speed up this process further, but they are [likely a scam](https://aquariumscience.org/index.php/2-8-bacteria-in-a-bottle/).

> Note: When you use this method, the food will be rotting as the bacteria processes it (might turn white) and it is possible for the tank to temporarily appear dirty. It should at some point stabilize and become clean again.

>Note: There are many methods to complete the first aquarium cycle. You can essentially do whatever you want.

On the other hand, I personally find that prospect dreadful. XD An empty fish tank sounds very boring. While not the "safest option," you can also just... immediately put the fish in. That's what most people do. I don't have enough experience to tell you just how great the risk of the fish dying is, but it appears to be small, at least so long you're not overfeeding them and having good filtration and aeration. And if you're not starting out with some finicky or expensive fish, not only will they likely be poised to survive it, but you can also just sort of easily replace them in the awful scenario where that happens. XD I didn't have much of a choice, but my fish went straight in and they seem to be fine.

> Let's remember that people get goldfish and put them in small bowls and do that for months without the fish dying. In fact, when I was little, that's exactly what happened with the goldfish my grandmother bought. The fish eventually died after a few months because it actually jumped out of the bowl at night. I should say that I am by no means saying putting fish in bowls is what people _should_ be doing.

Read more about the nitrogen cycle: https://aquariumscience.org/index.php/1-1-2-a-simple-way-to-cycle/


## The Filter
The filter is an important part of the aquarium, and the good news is that it usually comes preinstalled or bundled with new tanks.

Here is what the filter does:

1. Removes visible debris and waste, leading to less decomposition in the tank.
2. Supports bacterial colonies in (bio)**filter media** (usually the "sponge" part of the filter that also acts as a mechanical filter against that debris), which is by far the largest source of accumulation of beneficial bacteria in the tank. **Be cautious about replacing or cleaning filter media because it's part of the nitrogen cycle. The filter medium is supposed to be dirty. Only rinse at best. Replacing with new filter media, if necessary at some point, will mean partially restarting the nitrogen cycle.** Read more [here](https://aquariumscience.org/index.php/1-1-6-filter-media/). Note that debris can build up and literally clog your filter (usually hang-on-back filters), so cleaning that debris is sometimes necessary.
3. When coupled with an air pump, which is most often the case, creates **oxygenation/aeration** and water movement that allows the chemical composition of the water to be distributed evenly around the tank and circulation allows for no part of the tank to allow waste accumulation.

You definitely do not want stagnant water. While you can technically do without a filter and/or air pump, you'd have to change water much more frequently.

![image](https://hackmd.io/_uploads/ByEMOMZXyl.png)
> <small>Image: Some hang-on filter. [Source](https://www.aquariumindustrial.com/new-products/power-filter-nano). The tube sucks up debris, and the sponge in this filter will accumulate large colonies of bacteria. I don't know if this filter has an air pump, but most tanks will have filters that do. If you lack an air pump, buy an [air stone](https://www.amazon.com/s?k=air+stone+aquarium&crid=KCTY6MGYW516&sprefix=air+stone+aquariu%2Caps%2C225&ref=nb_sb_noss_2). You can put a toy with an opening on the air stone and it'll look great. Like [these volcano things](https://www.youtube.com/shorts/AEnb9749BLg).</small>

It should be noted that **the more filter media surface area, the better**. So be mindful of inefficient filters.

> Note: Advanced: Just use sponges or K1 for filter media. You do not need any other type of filter. Read [more](https://aquariumscience.org/index.php/7-filter-media/).


### Types of Filters
If you're buying a filter, the type of filter you want depends on a few things. As far as I can tell, [sponge filters](https://www.amazon.com/s?k=sponge+filter&crid=396JKU5R016U8&sprefix=sponge+fil%2Caps%2C275&ref=nb_sb_noss_2) are cheap and great (and aerate by default), but they don't look as good as [hang-on-back filters](https://www.amazon.com/s?k=hang+on+back+filter&crid=ODREADIAWDG2&sprefix=hang+on+back+filt%2Caps%2C255&ref=nb_sb_noss_2) and internal filters. Sponge filters can look ugly if not hidden. If you have a small tank and only one, you should probably get a hang-on-back filter because space and aesthetics are important. There are also things like external filters (e.g. canister filters) but those are for really big tanks.

![image](https://hackmd.io/_uploads/HJARqVWXJe.png)
> <small>Image: Sponge filter vs hang-on-back filter. Thumbnail from [this video](https://www.youtube.com/watch?v=zU4i_jSV8LU) that summarizes the differences (15 min).</small>


#### Prefilter Sponge
In some cases, the intake tube at the bottom of a hang-on-back filter may have an inlet that is too large, potentially drawing in very small fish or shrimp. It may also suck up most the food in the tank (but that's probably a good thing).

That's when you can buy things like [prefilter sponges](https://www.amazon.com/s?k=prefilter+aquarium&crid=29US5KCTCCRWE&sprefix=prefilter+aquariu%2Caps%2C235&ref=nb_sb_noss_2). But otherwise it's not a necessity.

![image](https://hackmd.io/_uploads/Hyx8ZB-Qyl.png)
> <small>Image: An example of a filter that would need a prefilter sponge if you intended to keep cherry shrimp or very small fish.</small>


### Noise
Most filters make some noise. There are methods to deal with that, and I should look into them, but consider that a fish tank might be an audible item in a room.


## Aeration / Oxygenation and Water Circulation
As mentioned previously, you don't want stagnant water in your tank. It breeds bacteria and creates a toxic environment. Water circulation significantly improves your chances of that not happening.

So how will you get water circulation?

Through airflow, of course! We discussed how most filters have air filtration, but, to be fair, not all air pumps are equal. If the air pump is placed at 90° angle from the filter, you will get stronger circulation than if it was placed facing upwards. These currents can sometimes be quite strong, though, and some slow-moving fish like bettas can struggle with strong currents.

But the much more important part is aeration. There's the very basic fact that fish need dissolved air in the water to breathe through gills, and that the amount of air in water is depleted as they breathe it. So you need to introduce that air through air filtration.

There's also the fact that a well oxygenated tank is a clean and healthy tank. It's something about bacteria populations multiplying very quickly with plentiful oxygen, then consuming all the dissolved organic compounds at a quicker rate, and facing population plateau sooner as they are eaten by organisms up in the food chain. Explanation [here](https://aquariumscience.org/index.php/9-1-aeration-in-depth/).

So having a lot of bubbles is good. You also want the surface of your water to be disturbed.

A very simple way to increase aeration in a tank is to buy an [air stone](https://www.amazon.com/s?k=air+stone+aquarium&crid=KCTY6MGYW516&sprefix=air+stone+aquariu%2Caps%2C225&ref=nb_sb_noss_2). But if your tank is small and/or isn't heavily stocked, then you don't need them, so long you have at least one source of air filtration.

> Note: If the fish are "gasping for air" near the surface, it means there is not enough oxygen in the water. Or they might be sick.

## Fish
Go with freshwater tanks if you don't want a hassle in the beginning. Saltwater tanks allow for a much greater diversity of fish, but with freshwater tanks you've also got pretty much anything you want anyway. Shrimp, snails, colorful fish, crabs.

![](https://www.garnelio.de/media/image/8f/e1/e3/mix.jpg)
> <small>Image: Cherry shrimp (_Neocaridina davidi_) are selectively bred freshwater shrimp. They also come in green. You'll easily find them in the trade. They clean up additional waste in the tank. Note, though, that they are quite small, and some fish may try to eat them.</small>

![](https://i.redd.it/humc0rqwi06a1.jpg)
> <small>Image: Freshwater fiddler crabs.</small>

![image](https://hackmd.io/_uploads/HyqbniXXJe.png)
> <small>Image: Bladder snail.</small>


![image](https://hackmd.io/_uploads/Hk7_himmyx.png)
> <small>Image: Freshwater puffer fish (blowfish).</small>

### Coldwater and Tropical Fish
There's this distinction in the freshwater aquarium hobby between "coldwater" and "tropical" fish. In reality, most "coldwater" fish are eurythermal, which means you can keep them in pretty much any temperature you want.

> Note: All fish are more relaxed and live somewhat longer when you keep them in the lower range of their preferred temperature. (The same also applies to feeding.) It may be damaging to chronically keep them in temperatures that are too low, though. Idk.

> Note: People will recommend you "acclimate" your fish to the temperature of your tank slowly. So something like putting the bag with the fish in the tank to float for a couple of hours. I think you should practice this with expensive fish just to be 100% sure, but generally fish can tolerate water temperature change, so, lol. Even if they get "shocked," which most of the time they probably wouldn't, that beats having to wait hours to put them in. They'll be fine.

### Common Freshwater Fish in the Hobby
The most common fish I've encountered in beginner freshwater aquariums are (see an expansive [Wikipedia list with images here](https://en.wikipedia.org/wiki/List_of_freshwater_aquarium_fish_species)):

#### 1. Goldfish (Cyprinids), "Coldwater" (Eurythermal)
![](https://upload.wikimedia.org/wikipedia/commons/e/e9/Goldfish3.jpg)

Goldfish (_Carassius auratus_) are the oldest kept aquarium fish. Like their other _Carassius_ cousins, they're very hardy and can withstand terrible water conditions. They also happen to be one of the bigger fish in the hobby.

Now, you might hear two common "criticisms" of goldfish as beginner fish:
1. They grow too big (40 cm or 15") (for example [this big](https://www.sail-world.com/photos/sailworld/photos_2013_2/Alt_pb130221goldfish931p.photoblog900.jpg)).
2. They produce a huge amount of waste.

And the conclusion for both being that you need to give them a special amount of care and buy huge tanks.

Both of these assertions are **false**.

Goldfish, like other fish in the genus, release homones that stifle their growth in absence of enough physical space. How these hormones actually work is probably complicated and poorly understood, but do note that they are **not found in the water**. Some people will claim this is why they do water change. Having read about Prussian carp, their size ranges depending on how concentrated their population is and how large the pond is. So it's nothing unusual.

Your fish not reaching its maximum size potential is not unhealthy. The longest lived goldfish in captivity (somewhere around 40 years) have been kept in a small tank and are themselves small. Look at [them](https://www.guinnessworldrecords.com/news/2023/8/oldest-goldfish-ever-lived-so-long-his-scales-turned-silver-756781). If anything, they might actually live longer this way. Additionally, if at any point you decide to put them in a larger tank and up the food amount, they'll grow immediately. Also note that the more realistic "maximum" size for goldfish is more like 5 inches rather than 15.

Secondly, the amount of waste the fish produce **entirely depends on how much you feed them**. Goldfish are constantly in search of food and they will eat so long they can. Just keep it on the low side and you'll have no problem with bioload.

And finally, if goldfish were so vulnerable to poor water conditions, would they have been able to withstand centuries of cultivation in medieval China? Would Prussian carp withstand awfully dirty ponds all around Europe (and now Canada) and become invasive?

Now, a lot of breeds of goldfish have emerged over the decades (and centuries). Generally, the normal goldfish breed is called "common goldfish." You have breeds categorized into "fancy goldfish" (which are terrible swimmers and a bit cursed genetically). The latter have double tails. But then you also have fun breeds like telescope goldfish (which often come in black) and so on. Many of these will be available in your local pet store.

Goldfish are so versatile: they're not aggressive, you can keep them with as many other fish as you want (or alone, they're not schooling fish), they can live in any temperature, they're robust, etc. So they're a great beginner fish.

> Note: Goldfish _will_ eat animals (including fish) significantly smaller than themselves.

You can read the Wikipedia entry on goldfish care [here](https://en.wikipedia.org/wiki/Goldfish#Cultivation) (but note the article chooses to talk about some of these things imo incorrectly and doesn't provide sources anyway), and you can also read the entry on the Aquarium Science website [here](https://aquariumscience.org/index.php/17-5-goldfish/) and [here](https://aquariumscience.org/index.php/17-5-4-goldfish-care/).

#### 2. Danios - Zebrafish (Cyprinids), "Coldwater" (Eurythermal)
![](https://upload.wikimedia.org/wikipedia/commons/a/ac/Zebrafisch.jpg)

Zebrafish or Zebra danio, _Danio rerio_, is the most common danio fish in the trade. Peaceful and playful. Read more about care on [Wikipedia](https://en.wikipedia.org/wiki/zebrafish?variant=zh-tw#In_the_aquarium).

#### 3. Barbs - Tiger Barbs (Cyprinids), "Tropical"
![](https://upload.wikimedia.org/wikipedia/commons/thumb/2/20/Pandabarben.jpg/1280px-Pandabarben.jpg)

According to [Wikipedia](https://en.wikipedia.org/wiki/Tiger_barb#In_the_aquarium):
"The tiger barb, an active shoaling fish, is usually kept in groups of six or more. They are often aggressive in numbers less than five, and are known fin nippers. Semi aggressive fish form a pecking order in the pack which they may extend to other fish, giving them a reputation for nipping at the fins of other fish, especially if they are wounded or injured. They are thus not recommended for tanks with slower, more peaceful fishes such as bettas, gouramis, angelfish and others with long, flowing fins. They do, however, work well with many fast-moving fish such as danios, platys and most catfish."

#### 4. Tetras - Black Tetras, Neon Tetras (Characoids), "Tropical"

![Black tetra](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c4/Adulter_Trauermantelsalmer-Gymnocorymbus_ternetzi.jpg/800px-Adulter_Trauermantelsalmer-Gymnocorymbus_ternetzi.jpg)

![Neon tetra](https://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Neonsalmler_Paracheirodon_innesi.jpg/1280px-Neonsalmler_Paracheirodon_innesi.jpg)

- Black tetras according to [Wikipedia](https://en.wikipedia.org/wiki/Black_tetra#In_the_aquarium):
"A highly spirited fish that may occasionally chase its own species as well as harass slow moving fish with long fins. This fish is very hardy and can stand a variety of water qualities. Disease is not a big problem with the black tetra. The black tetra is also known as the black skirt tetra. The female black tetra is more robust and larger than the male."
- Neon tetras according to [Wikipedia](https://en.wikipedia.org/wiki/Neon_tetra#In_the_aquarium):
"They can have a lifespan of as long as ten years, but normally just two to three years in an aquarium.
They are shoaling fish and must be kept in groups of at least six, but will be more active in groups of eight to 12 or more. Neon tetras are best kept in a densely planted tank to resemble their native Amazon environments."

#### 5. Bettas (Labyrinth fish), "Tropical"
![](https://upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Kampffisch_betta_splendenscele4.jpg/1280px-Kampffisch_betta_splendenscele4.jpg)

_Betta splendens_, in particular, the Siamese fighting fish, is the betta I mean. Read about their care on [Wikipedia](https://en.wikipedia.org/wiki/Siamese_fighting_fish#In_the_aquarium). Another hardy fish that can tolerate poor water conditions, popular for a reason. They are slow-moving, very territorial (so recommended to only keep one _male_ at a time), and has pretty morphology. They come in _many_, _many_ colors and fin shapes. Prone to [fin rot](https://en.wikipedia.org/wiki/Fin_rot), but that probably happens rarely.

So, the main limitations with bettas, albeit pretty, is that they usually don't work well with other creatures in the aquarium, and most certainly not each other. They are also smaller than goldfish and swim slowly. Bettas can be a good choice, though.


#### 6. Guppies (Live-bearers), "Tropical"
![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/de/Guppy_breeds.jpg/800px-Guppy_breeds.jpg)

We are talking about the fancy guppy, _Poecilia reticulata_. One thing to note about guppies is that they've been overbred/inbred and may not be as hardy as they used to be. Still, I think it's a good choice. Small, cute fish.

Wikipedia says (read more about their care [here](https://en.wikipedia.org/wiki/Guppy#In_the_aquarium)):
"They generally need a ratio of 1 male to 2 females or more. All guppies and mollies are hardy fish that tolerate lower oxygen levels and temperatures than most aquarium fish, give birth to live young, and readily breed in home tanks. Can live in full sea water."

#### 7. GloFish® (several species)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/3/30/GloFish_tetra.jpg/640px-GloFish_tetra.jpg)

GloFish are genetically modified fish that are fluorescent (so you need a UV light. You can get GloFish's own LED lamp. You can also get GloFish gravel that is similarly fluorescent) and otherwise in unusual colors. They have tetras, bettas, danios, etc. Less healthy and more expensive than their natural counterparts, but probably quite interesting, especially to children.

![image](https://hackmd.io/_uploads/ByGiPUWmJl.png)


### Fish Sickness
The most common fish sickness is [ich](https://aquariumscience.org/index.php/10-2-2-ich/). It is easily treatable.


## Tank
The primary concern for the tank is size. Size will limit how much stuff you can put in your tank, how much care the tank will require, and so on. Questions to ask yourself:

1. How much space do you have?
2. Would you have a larger tank eventually? (How soon do you plan to upgrade, if at all?)

If you have a lot of space, maybe it's not such a bad idea to buy a larger tank. Just consider also that they get quite expensive. People easily spend upwards of $500 on a large tank. And obviously they take more maintenance.

On the other hand, nano-tank "kits," which range from 2 to 5 gallons (maybe up to 10?), are around $50 to $100 and contain most of the equipment you need, including a filtration system.

You are in any case looking to spend at least $100 for the most basic aquarium and fish. Can easily climb to $200.

If you buy used tanks, which can get _really_ cheap, you probably want to [reseal them with silicone](https://www.youtube.com/watch?v=-oejTE1QDUk). But maybe that's too much hassle and [risk](https://www.youtube.com/watch?v=qY2NXgp_yok). I don't know.

> Note: A lot of fish can jump out of the tank, and you also don't want water to evaporate. Make sure your tank has a cover/lid.

This 14-minute [video](https://www.youtube.com/watch?v=vOubuXdLIjs) summarizes a lot of aquarium care (though tailored for bettas and with some unnecessary products you don't actually need).

I come back from a comment in a later section of this text to say that my personal estimate is that you can get away with 1 goldfish-sized fish per gallon of water. It'll be a stockier tank.


### Water change
Water change is easy with a **siphon**. Probably worth getting. https://www.amazon.com/live/video/03de0f90ae884545b279a95072d698da?ref_=dp_ive_hero_0

As noted, changing 1/3 of the water every week should work fine.


### Lighting
Consider that direct sunlight is probably not great. One thing that both direct sunlight and LED lighting have in common is that they can encourage algae to form. So, having LED on all the time means more cleaning.


### Feeding
As stated earlier, do not overfeed your fish so that waste doesn't accumulate. I think it's hard to say how much you should feed since it depends on the fish, but note that many fish can **survive 2 weeks without food**.

Here are some easy guidelines you can follow:
- Only feed as much as the fish can eat in 1 minute per day
- Only feed 2%-5% of the fish's bodyweight per day

It doesn't help, I know. Try to settle on feeding somewhere in the lower range. If your fish are active and quick, they're healthy. If they're kind of lethargic, they might be underfed.

I think a sensible amount of food you can feed per day can be found at [this timestamp](https://youtu.be/vOubuXdLIjs?t=767). Generally you should look at the size of your fish. That's a betta. They're feeding them 4-6 pellets, but obviously if it turns out somehow they're becoming lethargic due to underfeeding, increase the amount. 5 may be a pretty safe amount for this fish. Pellets are bigger than flakes, so probably worth putting more flakes if that's what you got.

![image](https://hackmd.io/_uploads/Hk3bwv5Qyl.png)


As for what types of food you can get, anything will do really. You've got the floating flakes, the pellets, the bloodworms, etc. You can feed regular vegetables, insects, etc. Easier to google your fish and what it can eat.

> Note: Some fish are more aggressive than others when it comes to eating, and may take up all of the food. Be sure that all fish are eating.


#### Auto Feeders
When you're away, or maybe every day, you can set up auto feeders like [these](https://www.amazon.com/Best-Sellers-Automatic-Fish-Feeders/zgbs/pet-supplies/2975462011) (and watch a video [here](https://www.youtube.com/watch?v=EHqfZDMt8cA)). Works better for larger tanks and I don't know how to install it with a tank with a lid.

![image](https://hackmd.io/_uploads/BymC0r5Qke.png)

There are also things like [feeding rings](https://www.amazon.com/fish-feeding-ring/s?k=fish+feeding+ring) that can help your floating food remain stationary on the surface (since a strong current will quickly remove them).


#### Fish Poop
Observing my Prussian carp, I can say that their poop is generally the color of their food. We've got multicolored flakes so it can be red, green, etc. When goldfish have very long, thin white poop, they might be constipated or starving. Hard to say. But it doesn't need to mean sickness, in any case.


### Dechlorinator (Water Conditioner)
It is recommended to get a water conditioner and dechlorinate tap water. While water chlorination is very beneficial for us humans, it is toxic to fish. Add the recommended amount or more before you do a water change. See [example](https://www.amazon.com/API-CONDITIONER-Aquarium-Conditioner-16-Ounce/dp/B004LO9KSY) of a dechlorinator. Read [more](https://aquariumscience.org/index.php/5-5-chlorine-and-chloramine/).


## Substrate
You don't always need substrate, but it is probably good for increasing surface area (or something along those lines) for bacteria to process waste and definitely improves the aesthetic appeal of your tank. It can also just collect food waste, though.

For the most part, substrate you can buy is divided into gravel and sand. It is possible to get crushed limestone etc, but that's all in the "other" category. I don't think it matters much which one you get. People will talk about the possibility of fish "choking" on gravel if they can eat it (and they will certainly put pieces of gravel in their mouths if they can), but there is little evidence this is actually a thing.

Consider that you can get both sand and gravel (although more often gravel) in various colors. Black, blue, red, green, etc. 

If you take white (or generally very light) sand or gravel, and you don't have a nano-tank with a strong current and filter, **fish waste may be very visible**.

If you want to go cheap or already have a cat, cat litter can serve as great substrate.

![image](https://hackmd.io/_uploads/SkRu8wW7kg.png)
> <small>Image: Cat litter substrate. [Source](https://www.plantedtank.net/threads/have-kitty-litter-as-a-substrate-i-do-pics.55280/).</small>


## Decoration
You can put literally anything you want. Plastic, resin, unused toys. It's fun for fish to hide or go through confined spaces, in particular.

I'm currently a fan of very unnatural and colorful looking aquariums. Most people who keep fish for a while seem to converge on some kind of natural look. _Shrug_.

If an object is "sharp," fish may rub against it and lose a few scales. I'm not sure to what degree you need to care about this. Probably not at all, unless your fish is a bit more finicky. But at least you'll know why it happens if it happens. (I.e. it's not always sickness.)

Fish (like bettas) can also get stuck in holes that are too small for them. I suppose you should keep an eye for that. Also note that when you add plastic toys not meant for fish tanks, they may not be able to hold and may be "uprooted" from the substrate and float.

If you're going for a more colorful combination, think about which colors you want to combine. If you're gonna go all the way, even think about the color of your fish.

I like to think about complementary colors. My tank has light blue gravel and mostly green decor because I didn't think ahead. But perhaps a better combination would've been to have had reddish purple gravel. Maybe not—red gravel tends to look bad in aquariums. Instead, perhaps it would've been more interesting to have largely orange decor? And then in terms of contrast, darker decoration would've worked possibly a little better. Or, if you think about emphasizing the color of your fish, a darker substrate would make more sense.

![image](https://hackmd.io/_uploads/BkFBBvWmkl.png)

Or you can just mix a lot of colors.

![](https://i.pinimg.com/736x/47/a8/a3/47a8a3a622db79ddf998d16373622e73.jpg)
> <small>Image: You can buy all kinds of plastic plants off Amazon in various colors.</small>

If your tank is larger or has a bit more substrate, maybe you can consider one of these "undergravel" hideaways, like [here](https://www.temu.com/uk/natural-looking-aquarium-cave--abs-resin-fish-hideaway-bottom--tunnel-g-601099687794510.html). There's a few common types.

![image](https://hackmd.io/_uploads/Hy4mODZXJx.png)

Or have a floating island. Apparently bettas love these things. Like [here](https://www.temu.com/uk/floating-aquarium-decor-island-with-realistic-plants--abs---with-hideaway-caves-for-fish-tanks-turtle--platform-multi-use-aquatic-landscape-accessory-suitable-for-all-fish--g-601099593003204.html
) or [here](https://www.amazon.com/MWYZGmold-Aquarium-Decorative-Decorations-Interactive/dp/B0CZJDH4FS).

![image](https://hackmd.io/_uploads/H1ss_vW7kl.png)

In any case, fish will love things with holes in them. And places they can hide. But don't let them hide all the time! That's awfully boring.

Aquarium decor is typically expensive, so if you have old plastic toys laying around that could serve as great decor, do try to use them. At least I would.

The decor I bought was pretty simple. The fish kept going in and out, making circles around the wood, etc. (Later I threw in a bunch of toys—not included on the image.)

![image](https://hackmd.io/_uploads/SJHS9wbm1x.png)

### Some Examples of Well Decorated Tanks

This one is a video: https://www.facebook.com/mkimiii/videos/1118502046589865/?idorvanity=137026403136580
![image](https://hackmd.io/_uploads/HyYbyU57yl.png)

Another video: https://www.facebook.com/groups/320106974244685/posts/564072803181433/
![image](https://hackmd.io/_uploads/Hy5dkU5m1g.png)

Creative use of an airstone (video): https://www.facebook.com/StokieSalty/videos/1284279296031571/?idorvanity=320106974244685
![image](https://hackmd.io/_uploads/ByNj18qmJg.png)

An example of how some of these GloFish tanks look like: https://www.facebook.com/jen.drake.7967/videos/1132956418398719/?idorvanity=320106974244685
![image](https://hackmd.io/_uploads/Sy1AkLq7kl.png)

You may also look into some kind of "background" for your tank in the back. Take a [look](https://www.amazon.com/aquarium-background/s?k=aquarium+background).

![image](https://hackmd.io/_uploads/B11mRv9QJx.png)


## "What Tank Should I Get?"
Note that much of the equipment and fish listed so far can be bought at a local store. You could give it a visit and decide there.


#### Equipment 
The equipment you'll probably want, **some of which may come with the tank you're looking at**, will be:
- A fish net
- Maybe a heater (and thermometer)
- Fish food
- Dechlorinator / water conditioner (ideally)
- A siphon (ideally)
- A filter
- An oxygenator (air pump or air stone)
- A lid (because a lot of fish jump out and water evaporates)
- Some aquascaping tools ([like so](https://www.amazon.com/Aquascaping-Kit-Jeimier-Aquascape-Stainless/dp/B0C8G65ZCF)) will make things simpler, and the metal scraping tool for algae (if you get any algae) might not be ideal, so you can attach some sponge on it or use a tooth brush (watch [this](https://www.youtube.com/shorts/mjvuLsUq2Zk
))
- Some decoration
- Gravel or sand or... cat litter
- Fish (and/or shrimp, snails, crabs)

I think, as beginner with modest budgets, you're looking at 2 options:


### 1. Nano-tank
Choosing a nano-tank _especially_ makes sense if you don't have a lot of empty space around. You can consider these "desktop aquariums"—because they can literally fit on your desktop—and their biggest drawback is simply that they're limited and not very modifiable. On the other hand, they're convenient and look good, not to mention require little maintenance.

Here's a [YouTube short](https://www.youtube.com/shorts/j81pmdvK0qo) of various nano-tank designs. Notice the preference for goldfish.

> Note: Nano-tanks still need to be assembled when you receive them. It's not a lot of work, but the instructions that came with the nano-tank [I bought](https://www.amazon.de/dp/B074DWKSSG) here in Europe were incomplete and led to frustration. I had to watch [this video](https://www.youtube.com/watch?v=nXRPPliU_aM) to assemble everything.

>Note: Some of the following description pertains to one of the more common types of nano-tank. Each of the Amazon examples listed at the end are different from each other.

Here's my experience with _my_ nano-tank:
Sometimes on the louder side. This is because both the air pump and the filter are strong. The current created in the tank is also strong. That limits your choice of fish. Bettas swim too slowly, for example. 

Another "issue" that pops up is the filter inlet size. In my experience, that thing scoops up most of the waste in the tank quite efficiently. The water current guides waste into the filter and the holes are big enough to take anything in. 

This also means that a lot of the food you throw in will end up in the filter. Even the floating food. That's, again, actually a good thing because people overfeed their fish—but you could also be more efficient. What you can do is turn off the filter (simply pull the plug from the outlet. (And btw, you'll have 2 plugs: one for the LED lights, and one for the filter)), throw in some food, let your fish eat for a minute, and turn it on again. Everything they don't eat in that time can be discarded anyway.

You might not have a lot of space for a heater, and you probably wouldn't want fish that are too small. You might not be able to fit in an auto-feeder either. (I don't know.)

In that case, I think a very suitable choice for this type of nano-tank is a goldfish. The normal kind of goldfish, not the double-tailed freak (although: there are also some interesting goldfish breeds that aren't terrible swimmers). You can even put 2 in there if you want, though you probably would be stocked up if you only got a 2 gal version. I'd say aim for one goldfish sized fish per gallon. You can add up some smaller things in there as additions.

The fact is that you're going to be limited. If you _know_, deep in your heart, that you're only getting like a couple fish and that's it, then a nano-tank is perfect. But if you're going to be feeling like you could upgrade after 6 months, then maybe you could start off a bit bigger.


#### Nano-tanks on Amazon
Here are some aquariums on Amazon:

- GloFish tanks. 5-20 gal, $50-$150. Rated 4.1. Probably very fun for kids to have that UV light on and those fish. Although I wonder if most tanks have some sort of LED light that would work for GloFish. Have a look: https://www.amazon.com/GloFish-Gallon-Aquarium-Lights-Heater/dp/B013BXE1XO
- FZONE 1.2 gal tank. I honestly feel this one is genius for how small it is. The filter is quiet and hidden in the back. Genuinely a mobile tank. 4.5 stars. Seems to be $50 when not on a Black Friday sale, but is currently at $40. Check it out: https://www.amazon.com/FZONE-Adjustable-Filtration-Detachable-Invisible/dp/B0CT7X4T99
- MarineLand 3-5 gal. 3 gal is $66. Seems to be one of the best rated nano-tanks. 4.4 stars. The filter is quiet and the water circulation seems slower (I don't know if that's really bad, though). Both are hidden in the back. This kind of tank is perfect for a betta. Check out this [video review](https://www.amazon.com/gp/customer-reviews/R2LGR2RVBWFWWZ?ref=dp_vse_ibvc_sml). I would almost say that this may perhaps be one of the best options, especially for non-goldfish fish. https://www.amazon.com/Marineland-Contour-Glass-Aquarium-Light/dp/B00GOFSB6U
- COOSPIDER 2 gal. $43. 3.9 stars. This is the exact nano-tank design I have, with all of the flaws and benefits it has. I don't know if it competes with some of these other tanks, since I don't have them to see _their_ flaws. It has good aeration and should be less work to clean, though. I've seen one complaint about a leak after 4 months. Not sure if that's actually a thing, you'd probably find reviews like that anywhere. It is not recommended to totally decrease airflow because the filter will struggle and thus may eventually break down, so it will have to remain noisy. Funnily enough, it is advertised as a betta tank, and that's precisely what it's not! The more expensive version with a thermometer display can be found [here](https://www.amazon.com/Adjustable-Filteration-Oxygenation-Circulation-Leak-Proof/dp/B0DLWC9NZ5). Here's the link for COOSPIDER: https://www.amazon.com/Cleaning-Aquarium-Starter-Desktop-Decorations/dp/B09N6ZKRTR
- Then you have a bunch of 3 gal tanks elsewhere. Some of them come with a thermometer. Go through some of the reviews: [$65](https://www.amazon.com/Penn-Plax-Aquarium-Thermometer-Desktop/dp/B0069RPRHO), [$60](https://www.amazon.com/iPriro-Gallon-Aquarium-Separator-Multi-Functional/dp/B0DF7YJ15M), [$52](https://www.amazon.com/Tetra-Shaped-Gallon-Aquarium-Pedestal/dp/B008CA7W7E).
- And some 1.5 gal tanks, like this [one](https://www.amazon.com/Craftsboys-Gallon-Starter-Aquarium-Aquascape/dp/B0CJ4N48RY). But there are more.
- You can also consider more 5+ gal tanks, but I don't think anything above 10 gal is truly a nano-tank anymore.
- If you're European, German Amazon will more-or-less only have the 2-4 gal Nobleza tank [I bought](https://www.amazon.de/-/en/Nobleza-Aquarium-Lights-Tropical-Aquariums/dp/B074DWJV2X).


### 2. Modest Beginner Tank
Just follow this 14-minute video: https://www.youtube.com/watch?v=vOubuXdLIjs


## "What Fish Should I Get?"
Honestly I don't know much about this one. I don't know how often the fish die too. I've seen comments about how people buy 6 neon tetras and then most of them die but there are a few that remain extremely resilient and live long. I don't know to what degree it is the fault of the owner.

Goldfish has main character energy, and it doesn't hurt that it's one of the most robust fish out there. The whole carp family is. And you can get a few of them.

Your kids will remember the goldfish as a pet (as they would a betta, to be fair). The schooling fish are not pets as much as... aesthetic decor?

But there is a lot of choice out there. Maybe goldfish are a little too vanilla? 

The local fish store is a good idea to check what's out there, and don't refrain from talking to the employees. Ask whether the fish can handle cooler temperatures. Consider getting a small heater, maybe, if you're not getting eurythermal fish.

Generally I think if you're buying like simple fish for your kids, bettas and goldfish are good to start with.


## Closing Remarks
Ultimately, just use common sense and react to your unique circumstances. Try to put a tank away from expensive electronics, don't put it in a room where the floor is easy to damage by water (if you can help it). If waste accumulates at the bottom, consider cleaning it. If the fish are sick or lethargic, think about whether they're sick or whether it's something you've been doing. If the tank is new and suddenly very dirty, don't feed for a few days or make more frequent and larger water changes, etc.