I run my RR153 without sponges with 2 litres of biopellets (not AIO)... Every week, I flush the system by shutting down the system, then take out the top plate to wash... This is due to the deposits (white sticky film) forming above the top plate... The outflow tube might also get choked... So I blow the tube to get the deposits out...
I also realise that when the tubing gets choked, the outflow stream reduced dramatically... But once I blow out the deposits, it works brand new...
Although a bit demanding at times, but I'll have to say that it serves its purpose well... It's linked to my FOWLR, so I only bother about nitrates... And nitrates are really undetectable...