Review on 🐧 Optimized Penguin Power Filter Rite-Size Cartridge by Marineland by Jen Linares

this is the only filter selection I know of that fits. I didn't try to look for alternative brands. I have two goldfish and about 12 char in a 20 gallon aquarium. Filters last 2 to 4 weeks - not sure as I don't keep track of when I change them. I only change them when they are clogged. You can vacuum them up and reuse them once or twice, but that takes away from their useful life and doesn't last forever. You must rinse the filters before using a new one (otherwise a lot of black dust will come out). However, you cannot use chlorinated tap water. I use tank water but you can use purified water. In addition, some activated carbon granules fall out when rinsing. If you look inside the box you will see dust and occasionally granules. a little dirty. It's really annoying to flush them first, but what other choice do we have.