Thomas, I dont have any secrets. The best to ask fishes
Seriously, Idont know - perhaps, there is desert of filtration, perhaps that fishes are alone, perhaps it depends on dimension of aquarium, etc.
Thomas, everything I will describe exactly into next "MAGAZYN Tanganika". Probably, it will be translate on English.
I would like to write more, but my English is ... - very, very sorry
All the best