I would only use a canister or wet/dry system on my tanks. I'd the under gravel filter thing, the hang on the backs, all were awful. My water stats have always been right and I have always had clear water with them. However, as far as activated carbon, i never use it. There's been a lot of controversy as to whether it causes hole in the head disease in cichlids and it can become lethal to fish if not changed regularly. also, when you use a medicine, it can actually remove the medicine from your tank so you have to take it out. I use mechanical and biological filtration in my tanks. This system in my canister filter has always worked, even with my large waste producers. My aquarium is also very clean. Once I stuck mine on, I noticed a change within 2 hours. Are they worth it? Yes. they give you clear water, are excellent at cleanliness, the spray bars create a lot of oxygenation, and they last a long time. Canister filters also offer a wide range of choice as far as media goes. Like have mechanical and biological filtration in mine. I chose Eheim canister filters. I used Marineland once, and it sucked. The thing practically fell apart on me.
