I have four guppies. I'm pretty sure they are all males. I moved them into a smaller tank in the middle of June. They we're all in a bigger tank with some others in my classroom.

It seemed like they were all fine at the beginning. There was a little bit of behavior between two of them that seemed aggressive but now they occasionally playfully fight (I think it's playful). And three of my fish all get along and seem to acknowledge each other.

But then my fourth fish spends most of his time under the plants and in the corner on the ground by the heater. He is still eating, but when I drop in food he very slowly floats up to the food, and seems to be ignored by the others.

I have done research but can't quite tell what's wrong. After he comes up for food he just floats for a little then plops back down to the floor but not in the corner. I'm not sure if he is getting bullied, stressed, or is sick.

  • 2
    Did you cycle you aquarium before putting the fish inside? Have you done a water test recently? If no, please the water water quality (can also be done at many pet or aquarium shops). If yes, please edit your question and add the result of the latest water test. Such behavior can be a sign of bad water quality.
    – Elmy
    Aug 9, 2022 at 10:53

1 Answer 1


Hmm, having poor control over buoyancy sounds like it could be Swim Bladder Disease. Some fish really are shy but guppies are generally not shy, so if this fish wasn't shy before, it could be hiding because he feels more vulnerable being sick.

Do you have a "hospital tank"? You might consider putting him in a separate tank in order to administer medicine for this fish, such as MelaFix, which is a broad-spectrum medicine (and stinks quite a bit). This way, only the sick fish gets medicine. Remember that hospital tanks still need aeration as guppies don't breathe from the surface.

As the fish recovers remember to do your water changes regularly, and to test the tank water conditions.

Additionally, if you got the fish recently, some stores have a policy where you can return fish that die soon after purchase as they might have been sick before you purchased them. Check your receipt or call the store to find out what your options are.

It sounds like this fish is sick but has a great chance at recovering.

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