my 10 gallon nano tank has just finished cycleing. I bought one 4 striped damsel and on the first day it was doing ok. but it was hiding behind the fikter a lot. my damsel on the second day was swimming kinda funny. kinda side ways. it stays at one spot for a few seconds leang a little to the right and left. then it goes off and swims fine. i got it at petco and it seemed fine at the store tank. i kept the tank water from the tank at the store in a bag just incase of anything happening. Do you know whats happening to my fish? is it stress? i tested the water from petcos tank and i tested mine the results were exactly the same. but there was this one time i changed the filter and this black liquid was floating on the tank water then a few mins later it disapeared. (but i dont think that has anything to do with it) please help me!!!!!