What are the best compact or portable aquarium filters?

Compact air-driven sponge filter designed for 2-5 gallon tanks that provides mechanical and biological filtration via a sponge and built-in media; requires a separate aeration kit to operate. It's small, easy to install and maintain, and marketed as quiet for betta, shrimp, and nano setups.

The AquaClear 20 is a small hang-on power filter with a 100 gph max flow and adjustable flow control, supplying mechanical, chemical, and biological filtration via foam, carbon, and BioMax. It uses low power (6 watts) and a compact media basket that accepts supplied media and optional media types, making it easy to maintain for small aquariums. Suited for 5-20 gal tanks.

The Fluval AC20 is a compact clip-on power filter with a 4-stage filtration system (mechanical, chemical, biological) and an adjustable flow up to 100 US GPH. It includes pre-filter sponge, bio-foam, biomax and activated carbon, low wattage motor for energy efficiency, and is designed for quiet operation and easy media access. Suited for small freshwater or saltwater aquariums.

The Fluval AC30 is a clip-on power filter offering 4-stage filtration with included mechanical, chemical, and biological media and adjustable flow. It delivers 150 GPH and is designed for quiet, efficient operation with easy media access and CycleGuard independent media replacement. Suited to both freshwater and saltwater aquaria.

The Fluval AC50 is a clip-on hang-on-back power filter offering 4-stage filtration with mechanical, chemical and biological media included, adjustable flow control and a patented refiltration system for improved water contact time. It's whisper-quiet with redesigned motor/cover, CycleGuard to protect beneficial bacteria and suits freshwater and saltwater tanks sized 20-50 US gallons.

The Cascade 700 is an external canister filter providing mechanical, chemical and biological filtration with two large media baskets, a push-button primer, flow control valves and quiet operation. It delivers 185 GPH flow, runs on 25 W and includes starter media (floss, sponge, carbon), making it easy to install and maintain. Suited for freshwater or saltwater tanks up to 65 gal.

The Seachem Tidal 35 is a compact hang-on-back filter with a bottom-to-top flow, adjustable flow control, self-priming pump, maintenance alert, and a large media basket that ships with Matrix bio-media and a foam pad. It suits freshwater and saltwater setups for tanks up to 35 US gallons and emphasizes easy, low-maintenance operation and customizable media choices.