I had a fluval 104 on my 10 gallon hex for over six months till I sold the thing. It was fabulous! First, if you dont take care of the flter, of course it will accumulate debris and make nitrates! Second, it was convenient to clean and take care of. All I had to was unsnap the locks, stop the flow, and take her apart. I did this evevry 2 weeks because of the amount of debris it caught in there. I swear that it was like a filter/protein skimmer combo it was so good! I loved it and would recommend it to everyone! If you can afford one, get it! You won't regret it!
By the way, I used the sponges, but not the carbon cause I didnt want it to absorb the nutrients I dosed the tongue coral. I used seachem matrix instead. The sponges I just rinsed out under water from the tank. All was well and clear- no problems. Just take care of the filter with cleaning and she'll keep your tank in top condition!