How big are aphids? I have little bugs, about the size of a small
grain of sand. They rest on top of the frogbit and are dark black in
color. Are those them? I always left them there, as I figured they
were a good source of free food for baby fish - I assume baby fish are
eating them, because I keep having new baby cherry barbs everytime I
look at the tank. If I disturb the bugs by blowing on them or just
opening the top they bounce around on the top of the water. I don't
know what else I can say to describe them.

Are aphids or the animals I describe harmful in any way? The leaves of
my frogbit are almost never brown, usually only one leaf or two is
brown, but it isn't enough to worry me.

I stopped supplementing for about 2 weeks and the frogbit leaves
started to turn brown, so I assumed it was just the nitrate and not
anything else. They were, however, putting out small new leaves, not
as large as normal leaves, but there was new growth. I did occasionly
dose potassium, but never dosed nitrate. Reason I stopped dosing so
much is that I ran out of CO2 and haven't gotten it filled yet -
plants are still fine, just a little extra algae is all.