I am fairly new to fish keeping kind of. I had my first fish for ten years, and did everything possible wrong. I kept a neon tetra by itself with no heater, no cycling no tap water conditioner, and replaced all the water at the same time. I was clueless. Since then I've read a lot and discovered I know nothing. I currently have six aquariums, which are for the most part doing well, except for treating a healthy fish with medication because I thought it was sick, and my sarpae tetras keep dying. I lose about one every 2 months. I've tested the water, and for the most part everything's fine, but my nitrates rise to 40ppm and my ph is getting low. I know that I'm feeding too much, but have no idea how much to feed. The 3minute rule doesn't work because I have huge fish tanks with aquatic frogs, tetras, live bearers and catfish. The catfish refuse to eat pellet foods that are meant for them. I have every type of fish food you can think of, but don't really know what or how much to feed. My ADF
's don't eat immediately, same with the tetras and catfish. My only other issue is cycling. I use whisper filters, with pre made filter cartridges with floss and carbon, when they are dirty and can no longer be cleaned they must be replaced. Some of my filters have sponges and others have plastic things with bristles. Is that where my beneficial bacteria are? Or do I need to do something different when I replace the cartridge?I'd appreciated any advice you have.