I have a 5 gallon tank with 2 female and a male guppy. (Fry if there were some would have been removed to another tank) I bought them approximately 4 weeks ago. One of them is already dead, it was on the bottom and it's spine was crooked, bent to about 90 degrees. The other female is swimming weakly and panicky. It seems to sink to the bottom. The male is doing fine. I checked the water parameters and they are fine. (0 ammonia, 0 nitrates, 0 nitrites) I don't know what's wrong, it's only the females, and they didn't seem to be pregnant.