I have 5 purple tetras and 3 neons. All have been doing well but they have stopped eating in the last few days. At feeding time, they are usually the first to start eating the flakes and brine shrimp enthusiastically. Tested the water and all levels are fine. I even let them fast for a day and tetras still not eating. Are all of them sick together?? They are swimming around and schooling. Not sure what's wrong. It's a planted tank. Do they eat plants and full from that? What should I do?