Review on 🐠 Marineland Bio-Filter Balls - Enhanced Biological Aquatic Filtration, Designed for All C-Series Canister Filters (Pack of 1) - 90 Count by Jessica Lange

I don't know how good they are because I haven't used them in a canister filter. I use a HOB Tetra i40 filter and there is room for these balls in the filter slot because they are actually very small, about the size of a ping pong ball. Anyway, I'm not sure if it's really that great or not, because I have activated charcoal, a scratch filter and a sponge filter in this shaft. but it's inexpensive and I wanted to try it as I have a small patio pond that is outside and gets a lot of dirt and sunlight (algae growth). They will swim but you can also put them in a mesh bag to keep them together and if you want them to be fully submerged you can use these balls to place a rock in the mesh bag to make them sink.