Well, to be honest with you, I'm not sure keeping GloFish in a tank that small is really a good idea. They're small fish, but they need to be in a school and really do need a lot of swimming room as they're incredibly active little fellas. It is necessary to keep them in an appropriately sized school (5-6 fish or more) which just isn't really doable in a 3g tank, so I think it might be best to return the fish you have, do a fishless cycle on the tank, and then get fish that could be kept in a tank of that size permanently. A betta would be nice, but you could also consider microrasboras, a dwarf puffer, shrimp, etc.
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