All of my fish except the plec are swimming at the glass. They aren't jumping. They're just swimming at the glass all the time. What is the deal? I tested the water and the nitrates are 40 in one tank which I'm working to lower, and there are hardly any in the other. Ammonia is 0, nitrites 0, the test strips say 6.4 but I don't believe that, and the test strips say the total hardness is 120. I don't know if I trust these test strips. But why are my fish doing this?