these are perfect prefilters. Not too coarse, nor too fine. The sponge holds up to repeated cleanings. I clean mine every 2 weeks and they save lits of food and gravel from ending up in my filter. I run these on every canister and HOB I own. Only negative is the plastic adapters are VERY fragile. BE VERY GENTLE WITH THEM, THEY USUALLY CRACK, BUT ARE STILL USUABLE. Manufacturer needs to fix this plastic, otherwise prefect.