I do not own a fountain kit but I use these fountain prefilters as a prefilter for my aquariums. I slip them over the intake tubes and cinch a zip tie around them to keep them from falling off. I wash them once a week during a water change. They are always full of gunk so I know they are doing their job. If you have shrimp, drop the dirty prefilters in a bowl as my cherry shrimp love to graze on these filters. That way you can put the shrimp back in your tank. Cheapest prefilters I could find plus the material is very tough and takes abuse. I slam them in the sink to dislodge the particles within the sponge. A super choice to prefilter water, keep baby fish and shrimp from being sucked into a filter, grazing area for shrimp. and provides some biological filtering if you allow the bacterial colony to grow and rinse with aquarium water.