Canister Filters
External canisters are the standard for planted tanks. Best for: high flow, large media volume, inline equipment (CO2 diffuser, heater).
Top brands: Eheim Classic 2217 ($150), Fluval 407 ($250), Oase BioMaster Thermo 350 ($350 — built-in heater).
Sized at 5× tank volume per hour. A 75-gallon planted tank needs 350+ gph.
HOB (Hang-on-Back) Filters
Cheaper alternative. Less flow, more surface agitation (which off-gasses CO2 — bad for high-tech).
Acceptable for low-tech tanks. Avoid for high-tech.
Top: AquaClear 70 ($35–60), Marineland Penguin Pro 350 ($45).
Sponge Filters
Cheapest option. Air-driven biological filtration. Excellent for shrimp tanks (no fry suction).
Inadequate for medium and large planted tanks. Use as supplementary filtration in larger tanks.
Air pump required: $10–20.
Internal Power Filters
Less popular. Take up tank space. Useful for nano tanks under 10 gallons.
Eheim Mini-Up, Fluval U-series.
CO2 and Surface Agitation
Surface agitation off-gasses CO2. For high-tech tanks: minimize surface ripple. Position spraybar to deliver flow horizontally below the surface.
Lily pipes (glass output) reduce splash and look elegant.
Filter Media
Mechanical: filter floss, foam pads. Catches particulates.
Biological: ceramic rings, bio-balls, lava rock. Hosts beneficial bacteria.
Chemical: activated carbon (removes tannins — useful in non-blackwater tanks), Purigen (removes organics).
Order: mechanical → biological → chemical.