I have had this tank setup for about 6 months. It's 20 gallons heavy plants. I have 3 dwarf puffers and 2 otos, with 5 small Cory catfish. There is a weird coloring on the surface of my water, anyone know what it is? And my puffers don't seem to be as yellow as the ones I've seen pictures of. Can anyone tell me if my water levels are ok as well? They have always been in the good ranges on the strip but today they seem a little off.