How Many Killifish In A 5 Gallon Tank? | Aquascape Addiction

How Many Killifish In A 5 Gallon Tank?

As an Amazon Associate I earn from qualifying purchases.

A helpful tank size guide for Killifish, including how many you can house in a 5 gallon tank. We also cover some housing essentials that are essential to give these colorful fish a thriving tank environment.

How Many Killifish In A 5 Gallon Tank?

Although these fish have a very mean sounding and intimidating name, they are actually quite peaceful, for the most part. They can be a bit aggressive towards other male killifish, but that’s about it. They are certainly very colorful.

Many people wonder, how many killifish in a 5 gallon tank can fit comfortably? Each Killifish requires at least 2 gallons of space which means you can house 2 Killifish in a 5 gallon tank. Be sure to only keep 1 male in the tank as they get aggressive towards other males.

Let’s take a closer look at kill fish tank size and other important tank requirements.

How Many Killifish Can You Have In A Tank?

Technically speaking, as long as you have a large enough tank, you can keep as many killifish together as you want.

With that being said, male killifish can be quite aggressive towards other male killifish, particularly during breeding season and if they do not have enough space to live comfortably.

Therefore, when keeping multiple killifish together, say if you want 4 of them, only 1 should be a male.

A female to male ratio of 3 to 1 should allow you to avoid problems with aggression, particularly if you follow the 2 gallons of water per fish rule which we discussed above.

Do Killifish Need To Be In Pairs?

Killifish are technically not schooling fish, so they can be kept alone if need be.

However, they do like to have some of their own species around, both for some company and because in nature, safety is in numbers.

Therefore, it is recommended that you get at least 3 or 4 killifish and house them together. They will be much happier if they have tank mates of their own species.

Killifish Housing Requirements

Before you go out and buy yourself some killifish, there are some important housing requirements which you should be aware of, so let’s go over these right now.

Water Temperature

Killifish are subtropical fish, which means that they prefer their water to be moderately warm, but not too warm.

Remember that exactly how warm the water should be will depend on the specific type of killifish.

For the most part, anywhere from 68 to 75 degrees Fahrenheit should be fine, with most killifish being able to easily survive in water that is 72 degrees.

In all likelihood, this means that you will need a decent aquarium heater, and an aquarium thermometer to keep track of the temperature.

Water Hardness

Once again, exactly how hard or soft the water needs to be depends on the exact type of killifish.

For the most part, these fish prefer the water to be quite soft, with a dGH level no higher than 10, and for the most part, no lower than 7.

These are hardy fish and as long as you keep the water hardness level within or even close to these parameters, your killifish should be fine.

Just be sure to do some research on the exact type you have. You may need to purchase some water conditioners.

Water pH

Just like with water temperature and water hardness, how acidic or alkaline the water needs to be for killifish will depend on the exact type.

However, for the most part, these fish prefer their water to be slightly acidic, with the majority of them preferring a pH level somewhere between 6.0 and 7.0.

You will want to do some research on the exact type of killifish you have, and you definitely want to get yourself an aquarium pH testing kit as well.

Filtration & Aeration

When it comes to aeration, killifish do prefer having a good deal of dissolved oxygen in the water. If you have a small tank, it is recommended that you get a small air pump and/or airstone.

Moreover, these fish are quite delicate in terms of water quality, or in other words, they do need the water to be fairly clean.

For this reason, you do need a good filter that engages in all 3 types of water filtration, which includes mechanical, biological, and chemical filtration.

For a 10 gallon killifish tank, having an aquarium filter that can handle about 30 gallons of water per hour is recommended.

However, keep in mind that these fish do not like strong currents, or really any current at all.

Therefore, something like a hang on back trickle or waterfall filter is recommended. These keep water currents to a minimum, plus they can also help aerate the tank.


Killifish aren’t huge on bright lights. They actually prefer their tanks to be fairly dim. No, they should not be dark, but definitely not too bright either.

A standard aquarium light, one with limited power, will do fine for these fish.


When it comes to substrate, the best way to go for killifish is with a combination of sand and aquatic peat moss.

These fish often love to explore the bottom of the tank and forage for food, and more importantly, if you want them to breed, they need soft sand or peat moss to lay their eggs and bury them in.

Yes, you can go for very fine gravel substrate, although this will not really make them feel at home, and it also greatly decreases the chances that they will do any breeding.


Killifish do like to have a decent amount of vegetation to swim through and hide in. Now, an issue here is that many aquarium plants need a lot of light, but killifish don’t like bright light. Therefore, you will need to use plants that can thrive in low light conditions.

This like java moss, java ferns, other and cryptocorynes make for good options. Java moss is particularly good for breeding because killifish can lay their eggs in it.

Many people also choose to provide their killifish with a few floating plants to provide some cover from above.

Rocks & Deco

Killifish also like to have a few rocks, hollow caves, driftwood, and ceramics around. They love to explore and they like to get a bit of privacy at times as well.

For a small killifish tank, a small cave and a small piece of hollow driftwood are recommended.

Tank Mates

One thing to note about killifish is that if you plan on keeping multiple males together, make sure to provide them with ample tank space and plenty of hiding spaces where they can get some privacy from one another.

Other than that, killifish, although the name is scary, they usually do fine with most other small and peaceful aquarium fish. Tetras make for some of the best killifish tank mates out there.

A Lid

The other thing that you need to consider here is that killifish are great jumpers and they love jumping out of the tank. You absolutely need to get a lid or a hood for your killifish tank.

Commonly Asked Questions

How Many Killifish per Gallon?

This depends on the specific killifish in question. That said, every fish needs 1 gallon per inch at the very least, and therefore, you won’t find many killifish that can survive in a single gallon of water.

Are Killifish Hard to Keep?

This also depends on the exact type of killifish you get. Some are very easy to care for and some are very hard to care for.

Are Killifish Aggressive?

Killifish can be aggressive towards other male killifish as well as other male fish which resemble killifish, but other than that they tend to be quite peaceful.

Can Killifish Live with Bettas?

No, bettas and killifish cannot live together as they are not compatible in the least.


There you have it folks, everything you need to know about housing some scarily named yet beautiful killifish.

They many not be the number one easiest fish to care for, but if you follow the tips and rules outlined today, you really shouldn’t have any problems.