I have a Top Fin 20 gallon power filter that suggests to use those crappy cartridges for the filter media along with a black sponge that it came with. Since I do not know much about filter media aside from the cartridges I am completely at a loss of what to do with my situation. The filter in the Top Fin 20 gallon is fine. I only have a betta in there right now. My problem is that the cartridges get covered in brown algae/slime and then the tank becomes cloudy and backed-up within 3 days of cartridge replacement. I don't want to replace the cartridges because I want the tank to cycle, but there isn't any other way around it. I need filter media that is going to be able to handle particles to keep the tank clean and water clear.
Tonight I cleaned the tank and did a 25% water change because the water was so murky. When I was dumping the water from the tank out, I noticed that the water looks green/brown in the bucket. I think the Flourish I've been using twice a week is partially to blame? Possibly? My plants are thriving, but the water is icky. The hood of the tank was even COATED in green/brown slime from where the bubble maker has flicked droplets onto it during the day and night.
Any advice or input on filter media would be amazing. I use carbon pieces in the cartridges, and I was using Ammo Carb in small amounts, too. I didn't put any Ammo Carb in the new cartridge tonight to see if it was the problem. I want some Cory Cats but I am afraid that they may make the water worse. I've had some before (with my betta) and they seemed to poop quite a bit. I tested the water with the API Liquid Test Kit and everything was zero.
Here is what the cartridges look like after just three days. P.S. That is clean, treated water in the bucket -- not the green/brown kind I mentioned. That was probably obvious, though. Haha.
Sorry the picture is blurry.