“Not using mechanical if it’s hard to get to in the overflows.” I like easy. If it’s difficult to get to the mechanical filtration in the over flows but easy in the sump then do all mechanical filtration in the sump. Mechanical filtration has to happen in my opinion. Just pick the easiest place.
I believe mechanical and bio filtration are equally important. But the most important filtration is water change. You must put in new clean water to really clean the water. All the other filtration is just marking time between water changes.
I saw a post of a guy in Thailand that used 100% water change because he lived on a river and got free water. Did not use mechanical or bio filtration. He just turned over 100% of the water in his tank every couple hours.
What I’m saying is water changes are the only real filtration option we have. The other filtration options we have just marking time between water changes with out killing the fish.
I’ve never had bio balls clog. You can do mechanical before or after bio balls. Choose what’s easiest.
