Mine has collected some small particles of sand in it as well as a little bit of dietrus. I take a syphon gravel cleaner and syphon it all back into the refuge, to let it break down in there where it can be taken care of quickly. One way to prevent that is to place some type of filter in line with the overflow, I have a simple filter cut to fit into the tubes, then the water goes into the refuge through baffles into return or back into the refuge via skimmer.
Coffman