How many GloFish can go in one 2.5 gallon tank? I am seeing if I can fit 5 in a 2.5 gallon tank. Can I?
An aquarium that small is suitable only for some miniature shrimp. It does not have enough swimming room or biological load capacity for glofish. A ten or 20 gallon tank would provide a much safer environment.
No, you cannot.
As johnarthur wrote—I am just adding a voice to the chorus—a tank that size is not suitable for any single fish, much less a group. You just need to go for a larger tank, a 10 gallon at the very smallest. GloFish, however, are genetically modified zebra danios, which are very quickly swimming fish who need a lot of horizontal swimming room to be happy and healthy, so a 20 gallon would be much better.
And as hard as this may be to believe, the larger the tank, the easier it is to care for (until you get to the really massive ones).
Larger tanks are much easier to care for. I have so much less trouble with the 46, and the 30 compared to the 10's.
Please do consider a larger tank, and if you haven't already read up on the nitrogen cycle
No fish should be kept in a tank that small. It is too difficult to maintain a proper bio filter and the fish will suffer. I know there are specially designed glofish tanks that are that small, but they are not safe and appropriate for fish.
The glo danios are genetically altered zebra danios, and you have likely been told how hardy they are. Zebras are very hardy, but it has been my experience that the glofish are not as hardy as the regular zebras. Whether this is due to inbreeding or immunological compromising from the genetic manipulation, I'll let others debate. Regardless, glofish are not as strong as there counterparts, and no fish does well in such a small tank.
Unfortunately, the short answer to your question is 0.
I do know the right answer to this, but rather than rewrite gloman's post, my answer's exactly the same.
Tank's too small for most anything permanently, except maybe a killi (don't!) and GoFish are not particularly hardy in the long haul. After 6 months one of four electric greens I've had is alive and it has balance problems now.