The best filter depends on your tank size, livestock, and maintenance preferences. Three common types cover most hobbyist setups: hang-on-back, canister, and sponge filters.

Hang-on-back (HOB) filters clip onto the rim and pull water through replaceable cartridges or customizable media baskets. They are affordable, easy to maintain, and ideal for tanks up to about 55 gallons. Most provide decent mechanical and chemical filtration, though biological media capacity is limited compared to canisters. Popular models allow you to swap cartridges for ceramic rings and filter floss to boost bio-filtration.

Canister filters sit below the tank and push water through stacked trays of media. They offer superior biological, mechanical, and chemical filtration and are the go-to choice for tanks 40 gallons and larger, heavily stocked setups, or planted aquariums that benefit from strong flow distributed by a spray bar. Canisters are quieter once primed and need cleaning less often, but they cost more upfront and require more effort to open and service.

Sponge filters are the simplest option: an air pump drives water through a foam block that harbors beneficial bacteria. They excel in breeding tanks, hospital tanks, and nano setups because they provide gentle flow that will not trap fry. Sponge filters are extremely inexpensive and nearly silent, but they lack chemical filtration and can look bulky in display tanks.

For most beginners with a community freshwater tank in the 20 to 40 gallon range, a quality HOB filter rated for slightly above your tank volume strikes the best balance of cost, ease of use, and performance. Upgrade to a canister if you plan to keep messy species or want longer intervals between maintenance sessions.