Hey everyone, I've been into fish keeping for about a year and I've been trying to aid my best friend's dad as he is now binge buying for his fish keeping. They already have 4 aquariums in their house which I think is great, but he's set on turning his son's 10 gallon into a sump for his 55 gallon. The 55 currently has 2 Oscars, which he knows won't be sufficient forever, and a brown bullhead catfish. The tank's filtration is, as of the post being made, two 75 gallon Aqueon HOBs, and he does 30% water changes every week or so. I don't know what to recommend besides either a sponge filter or just buying a canister filter. I don't know his water parameters (bacterial), but his temperature is 82 degrees and his pH was ~6.8. I hope this helps, if anyone could give me some points to acquire just so I could tell him if it's worth it or not. Thanks in advance!