New and clueless

[Vegetarian fish nut]

Hi,
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.
Thanks,
Fish nut

[butterfly_koi]

Hi and welcome to AA! I think that the problem in your tank is due to the cycling issue which it is a good thing that you joined us! There are many many people here that can help you with that

[George9]

I don't even change media even when it can't be cleaned. Just get all the gunk out and put it back in. Only replace if it's falling apart. The media is what The good bacteria grows on that will break down fish waste. When you cycle the tank, you're building up you bacteria colonies. Are you cycling with fish, or without?

Welcome to AA!!

[Vegetarian fish nut]

My tanks have been running for about a year. I thought they were cycled, but I've been replacing the cartridges whenever their dirty, and won't rinse off. I bought an ammonia test kit, and found out my ammonia is at .5. What should I do when the cartridges start to fall apart? Also, the intake and inside the plastic filter box is full of gunk. Should I clean it or leave it?