Key Definitions
Mechanical filtration — removal of solid particles (organic sediment, fertiliser residue, dead organic matter, root hairs) through physical barriers.
Biofilter — a material or structure where nitrifying bacteria colonise the surface, increasing total colonisation area and serving as a microbiology reservoir.
Organic load — the quantity of organic compounds entering the solution per unit time from additives, dead tissue, and root exudates.
How Bioponic Filtration Differs from Aquarium Filtration
In aquariums, organic load is predictable. Bioponic systems deliberately introduce larger quantities of organic matter on a regular basis — fish meal, hydrolysates, vermicompost tea — plus dead root material and substrate residue.
Critical difference: aquarium filters aim for maximum water clarity, whereas over-filtration in bioponics can eliminate beneficial bacteria and reduce nitrification activity. The goal is controlled removal of harmful particles without destroying beneficial microbiology.
Two Filtration Levels: Mechanical and Biological
Mechanical Filtration
For systems of 100+ litres: use a settling tank or mechanical pre-filter before the main reservoir. Simple design: a first chamber where water slows and solids settle, then overflow to the main tank. Clean every 3–7 days depending on load.
For smaller systems: a mechanical pre-filter with a mesh bag or basket at the pump inlet. Target pore size 100–200 micrometres.
Biological Filtration
Biofilter media provides a large surface area where nitrifying bacteria establish colonies. Functions: increasing the total active surface for nitrification and serving as a microbiology reservoir.
Materials: plastic "reef blocks" or K1 media (polyethylene granules with developed surface area), ceramic rings, foam granules. Position in the solution flow, never in stagnant zones. Never clean aggressively — rinse only with system water to preserve bacterial biofilms.
Settling Tank: Simple Mechanics That Solve Most Problems
A settling tank is the most effective and cost-efficient solution for systems of 100+ litres. A retention time of 5–15 minutes at working flow rate is sufficient to settle most particles of 50+ micrometres.
Tank base: smooth material for easy cleaning. A 20–45° floor slope toward the drain is helpful where possible.
Biofilms: Problem vs Resource
Biofilms on pipes and nozzles (where flow must be clear) are problematic: they narrow passageways, become anaerobic in thick layers, and are a source of pathogens.
Biofilms on biofilter media are resources — this is exactly the nitrifying microbiology that is needed. A controlled biofilter surface redirects bacteria away from pipes and nozzles.
Three Most Costly Mistakes
- Aggressive cleaning of the biofilter or using chlorinated tap water: removing bacterial biofilms means losing the nitrification reservoir. Rinse only with system water — never tap water.
- Neglecting regular cleaning of the mechanical pre-filter: clogged mechanical filters become anaerobic — organic matter rots, producing toxins and pathogens that re-enter the system.
- Using a single filter for both functions: aquarium foam performs both mechanical and biological work simultaneously, but requires regular washing (which destroys the biological function) or becomes clogged and anaerobic.
Signs of Correct Filtration
- Nozzles and pipes remain clean for at least 2–4 weeks without cleaning
- The settling tank collects visible sediment that is easily removed
- Nitrification indicators are stable (NH₄⁺ low, NO₃⁻ rising)
- Fish meal dosing does not cause sudden turbidity spikes or sediment accumulation in pipes