I have a 125 gallon tank with an African walking catfish about 15 inches long and two Pacu that are 12 inches and about 7.5 inches tall. My amiracle wet dry that came with the tank cannot keep up. So I purchase on line a FX 5 (new). Heard great reviews thought that would solve my problems. To some extent it does, but cleaning the sponges take forever they get a really slimmy brown crude on them after a week of running I have nothing in the middle of the FX 5 yet. Is this normal to get this crude after a week am I suppose to clean more often? If this is the case I am not so fond of the FX 5. Then again maybe I am using it wrong, any advice would be great. Should I build a bigger sump? I see all these really clear tanks and mine is always a tinge of brown. The snails are thriving in this filter LOL figure they might help. I have no drift wood in the tank thought that might be the issue. I feed daily Xtreme Monster that I get from Kens.Thank you in advance.