rod, with a heavy bioload this will happen. I had about 2 dozen mystery snails in a 25g holding tank with the sponge filter as a prefilter attached to an HOB. I always knew when the filter needed cleaning once or twice a week because it would appear hour glass shaped from being clogged and the waterfall would slack off.
Shrimp don't produce nearly the same amount of biowaste as the snails did, and I haven't had a problem with the sponges on air..
Last edited by Soothing Shrimp; 01-15-2013 at 04:48 PM.