The main filter of my tank is doing very well. It is it's own little ecosystem...I have three different kinds if snails living in it cleaning up the solids in the crevices...they also end up dying in there when they get to big to crawl out. They decay and add nutrients & calcium back to the system - the eggs they laid hatch, and it starts over again. This clean up crew needs some help on the inside and on top where the snails don't go. I have some decaying vegetation and roots that could use some clean up - they are not growing any mold or fungus, which is good - so I figured I could leave them there for worms, and reep the rewards of worm castings for my system.