Help! 3 of 4 Black Skirt Tetras hiding, not eating
3 of 4 Black Skirt Tetras are suddenly hiding at bottom of tank and stopped eating. The 4th one still swims around normally and eats normally. They used to all eat together before. This has been going on for a week now. Ammonia is at 0, nitrites 0, nitrates 5, and Ph is 7.8. Tanks 77 degrees. It's a 12 gallon and the 3 are just staying under the cover of silk plants I have in there. They are the only fish in the tank and it has been set up for a little over a month. What could be going on?