Key Terminology
Sanitation — measures for cleaning and treating systems that reduce pathogen risk; fundamentally different from mineral hydroponics where disinfectants can be applied broadly.
Disinfectant — chemicals that kill microorganisms; standard agents (chlorine, hydrogen peroxide, ozone) destroy both pathogens and nitrifying bacteria.
Microflora — the community of microorganisms including beneficial nitrifiers, neutral saprotrophs, and potentially harmful pathogens.
Two Sanitation Models: Destruction vs Preservation
The "Destruction" Strategy
Full disinfection with aggressive agents between cycles. Result: a clean system, but 3–6 weeks are required to restore nitrification. Justified only in the case of serious pathogen contamination (Fusarium, Pythium, bacterial rot).
The "Preservation" Strategy
Minimal mechanical cleaning with gentle chemical control that preserves nitrifiers. Result: shorter inter-cycle periods with the microbial foundation intact. Suitable for normal cycle completion with no signs of pathology.
Gentle Sanitation: Methods That Preserve Nitrifiers
Mechanical cleaning — the foundation of gentle sanitation. Remove residual solution, flush pipes and reservoirs, physically remove sediment and organic deposits with brushes.
Low-concentration hydrogen peroxide (0.3–0.5%) — partial disinfection that suppresses some pathogens while preserving stable nitrifying colonies. Follow with a clean water rinse to neutral pH.
Plant-based and organic agents — grapefruit seed extract, garlic extract, and essential oils show antimicrobial activity against pathogens with relative safety for nitrifiers.
Heat — a hot water flush (55–65°C) destroys most pathogens and biofilms without chemicals.
Formation of Dangerous Biofilms
Dangerous biofilms form in anaerobic zones where denitrification replaces nitrification: nitrate is reduced to N₂ and hydrogen sulphide is released. A characteristic hydrogen sulphide odour indicates an active biofilm.
Common formation sites:
- Pipe dead ends and corners with slow flow
- Lower sections of NFT spray zones where liquid accumulates without aeration
- Thick organic sediment layers at the bottom of reservoirs
Prevention: design systems without dead zones, ensure circulation throughout, remove sediment regularly.
Full Disinfection: When and How
For confirmed pathogen outbreaks in the solution (Pythium, Fusarium, severe bacterial rot):
Chlorine (sodium hypochlorite, 200–300 mg/L active chlorine): After application — hold for 30 minutes, then flush until no residual chlorine remains. Neutralise with sodium thiosulphate.
Hydrogen peroxide (3–5%): Hold for 20–30 minutes, then flush with water. Breaks down to water and oxygen with no residue.
After disinfection, a full nitrification cycle is required: 3–6 weeks before the next planting.
Three Most Costly Mistakes
- Performing "preventive" full disinfection after every cycle without cause. This destroys microbial capital built up over months.
- Flushing the biofilter with chlorinated tap water after cleaning. Residual chlorine suppresses nitrifying bacteria.
- Allowing anaerobic biofilm to develop until the odour becomes obvious. By the time hydrogen sulphide is detectable, anaerobic zones have been active for weeks.
Signs of Balanced Sanitation
After cycle completion and gentle sanitation, nitrification indicators recover within 3–7 days (not 3–6 weeks). No hydrogen sulphide or persistent ammonia odours between cycles. Inspection of pipes and reservoirs shows a thin, uniform organic coating — not thick black or grey deposits in corners and dead ends.