The strength (performance) of an air pump for a 55-gallon drum biofilter depends on its airflow (CFM/LPM), pressure (PSI), and the biofilter's oxygen demand. Here’s what you need to know to choose the right pump for effective biofiltration:
Airflow (CFM/LPM) – Determines how much oxygen is delivered.
Recommended: 1.0–3.0 CFM (30–85 LPM) for a 55-gallon biofilter.
Rule of Thumb: 1 CFM per 50 gallons for moderate biofiltration (adjust based on bio-load).
Pressure (PSI) – Needed to push air through water depth and diffusers.
Standard: 1.5–4 PSI (most aquarium/pond pumps).
Deeper water? If the diffuser is >2 ft deep, a linear piston pump (higher PSI) may be needed.
Diffuser Efficiency – Fine-pore diffusers (e.g., airstones, membrane discs) require higher pressure but improve oxygen transfer.
Biofilter Media Type
Static (sponge, K1 media, bio-balls): Needs moderate aeration.
Fluidized (sand, moving bed): Requires stronger airflow to keep media suspended.
| Type | Strength (CFM) | Best For | Example Use |
|---|---|---|---|
| Diaphragm Pump | 0.5–2.5 CFM | Small to medium biofilters, low noise | Aquaponics, small ponds |
| Linear Piston | 1.5–5.0 CFM | Deep water, high oxygen demand | Large aquaponics, koi ponds |
| Rotary Vane | 3.0–10+ CFM | Commercial systems, high airflow | Large-scale biofilters |
For a standard K1 media biofilter:
Pump: 1.5–2.0 CFM diaphragm pump (e.g., Tetra Whisper AP 150).
Diffuser: 4-inch airstone or ceramic disc.
For a fluidized sand filter:
Pump: 2.5–3.5 CFM linear piston pump (e.g., *Hiblow HP-80*).
Poor water movement in the biofilter.
Media isn’t tumbling (for moving bed filters).
Low dissolved oxygen (fish gasping at surface).
A 55-gallon biofilter typically needs a 1.0–3.0 CFM air pump, with higher airflow for fluidized media or heavy stocking.
For most home systems: A 2.0 CFM diaphragm pump works well.
For commercial/koi setups: A 3.0+ CFM piston pump is better.