Can you fit three portions in a medium box?
I wouldn't worry too much. I normally go 3+ weeks (until output seems reduced) before cleaning my sponges. I'm sure that if I were to clean them weekly,
the shrimp may become lunch as well as the plants.you will need to do large water changes once a week.
your goldies probably did not get to their potential of 8" long because they were in an overstocked tank.they put off growth hormones that will stunt
Try pulling everyone out, re-arrange the tank a bit, then add them all back in. This should break up any established territories and put everyone on equal