I have just purchased a 10 gallon fish tank. I have one male betta and 3 tetras.

Two of the tetras swim around together but one of them stays at the bottom of the tank in the corner and looks like he's swimming but he's not going anywhere. I was told by the lady in the shop that it would be okay to not cycle the tank before adding them.

Any ideas on why he's doing this? Or any ways to help him?


2 Answers 2


This tetra is not feeling good. Likely because it doesn't have a group to school with. I'm assuming your tetras are neon tetras, but it's the same with some other tetras like cardinals.

Neon tetras are schooling fish, they need to be in a group to feel comfortable, the more the better. For best results you should have at least 12. For minimal requirements they should be at least 6. 3 is not enough and with such small numbers, often one of the neons will be bullied by another.

Anyway a 10 gallons is too small for a betta AND a school of tetras. It should be for the betta alone, he is enough for the 10 gallons territory, so you might want to consider giving the tetras back. Not all bettas are friendly enough to live with neons, but some are. However a 10 gallons cannot accomodate a full school of tetras.

Other possible reasons for its behavior:

  • The betta or the other tetras attacked it and he is scared. Tetras can be aggressive when stressed or not in sufficient numbers. Bettas are typically aggressive and territorial and like to fight other colorful fishes.

  • The tetra is sick or injured

  • The water quality is not good.

These are my ideas on why it is acting like this.

Now for ways to help him:

  • Provide your neons with an environment suitable for them: a big tank with plants and decorations and a group of more than 10 neons. With this you will witness their beautiful relaxed schooling behavior. They don't "group-up" all the time, only when they are startled. When they are calm and feel safe because of the group, they will disperse swimming around the tank. As it is, this stressed fish has nowhere to go or to be in the tank.

For a 10 gallons, a betta alone is one of the best, most interesting choices. Bettas have personality and are curious and smart, AND they like to be alone. Betta might coexist with some bottom dwelling fishes like catfish. Or snails.


I read the answer comments to your post before writing this, I understand the first answer has a link but what you must understand is that 10 tetras is a lot for a tank of your size. 3 is too small so I'd suggest 5. When it comes to schools you'll want to do them in odd numbers. Second, you don't need to wait 30 days to cycle your tank unless you aren't adding any beneficial bacteria. To shortly describe the Nitrogen Cycle to you, the nitrogen cycle happens when you have fish, when you first get a tank it goes through what is called "New Tank Syndrome" during this period of time is when you DON'T want to add fish, the reason being is that beneficial bacteria is needed to start the nitrogen cycle eliminating any toxins such as Ammonia, Nitrites, and Nitrates. How do you do this?? Well you can buy beneficial bacteria to start that process.

Say you just started your tank, set it up put all your decor and then water. Instead of putting fish in that day, you can go to your local pet store and pick up beneficial bacteria, I'd suggest API Stress Zyme, you'd also want to pick up Stress Coat which is a water conditioner. For the rest of your fish keeping hobby you'll want to use both whenever doing water changes, whatever bacteria you take out, you must put it back in. So you'll double the dose on your tanks first setup so say you have a 10 gal you'll want to treat it like a 20 gallon. You usually do both Stress Zyme and Stress Coat for the first 3 days THEN bring a sample to your pet store for testing. If all is good then get the fish.

If your fish is at the bottom it means it's stressed out either by being sick, not enough decorations, water conditions, or bullying. Stress Coat is a water conditioner but it also has aloe vera which puts the fishes natural slime coat back on it's body when it stresses out, eliminating any chance of getting sick.

I'd suggest more decor, more plants, and add some Stress Zyme and Stress Coat to your tank after doing a 10% water change, you'll only need about 10ml of each instead of the 20ml if you were starting a new tank.

Make sure you keep up on changing your carbon every month, you should be doing monthly water changes of 25% or weekly of 10%. Aquaclear is an amazing filter that I've used for years. Make sure you don't wash the sponge in fresh water but instead wash it in the tank water that you pulled out of the tank, it holds beneficial bacteria and if you wash it with fresh water you can shock the tank. The little bacteria ball things in the bag should also never be washed in fresh water.

  • changing your carbon every month did you mean water? Mar 31, 2018 at 22:39
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    No I mean carbon filter, if you have a filter in the tank it uses a carbon filter and carbon is only activated for a month so it needs to be changed monthly Apr 1, 2018 at 23:22
  • Changing activated charcoal filters monthly? I wasn't aware that was necessary. Apr 1, 2018 at 23:32
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    Yeah activated carbon is only good for a month and then it's no longer activated and not doing what it should be doing so it's good to make it a habit to change it out monthly. Personally I do 10% water changes weekly and on the 4th change I change the filter but some people change 25% monthly and at the same time change the filter. Apr 3, 2018 at 15:13
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    The nitrogen cycle doesn't get rid of nitrates, in fact it produces them while breaking down the ammonia and nitrite. Also when you say 'whatever you take out you need to put in' - that only really applies if you're taking out filter media or substrate. The bacteria is not free floating so doing a water change only will have no effect on the amount of beneficial bacteria you have in your aquarium. Therefore, adding more every water change is unnecessary.
    – Henders
    Sep 28, 2018 at 8:52

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