High nitrite in aquaculture systems
Nitrite accumulates when ammonia oxidation outpaces nitrite oxidation — typically during biofilter start-up, after restocking, following disinfection, or when loading has been increased faster than the nitrifying population can adapt. It is a system-maturity and capacity signal that deserves an infrastructure review.
Engineering and procurement guidance only — not a diagnosis and not veterinary advice. Multiple factors can produce the same reading; confirm findings with a qualified professional before acting.
Possible contributing factors
- Biofilter still maturing, or restarted after cleaning or disinfection
- Loading increased faster than the nitrite-oxidising population could adapt
- Low temperature or unstable pH slowing nitrification
- Alkalinity depletion limiting the biofilter
- Insufficient dissolved oxygen inside the filter media
- Organic overload from solids that were never removed from the loop
Plan the loading curve, not just the equipment
Most nitrite events on new systems are scheduling problems: the fish arrive before the biofilter is ready. A staged stocking plan tied to measured performance is part of the engineering package, and should be agreed before commissioning, not improvised afterwards.
Non-diagnostic scope
This page addresses treatment capacity and system design only. It does not provide veterinary guidance, treatment protocols or health assessment.
System areas to review
Biofilter design
Media type, specific surface area, contact time and hydraulic loading.
Start-up protocol
Documented maturation curve with staged loading rather than full stocking on day one.
Oxygen supply
Aeration or oxygenation dedicated to the treatment loop, not just the culture volume.
Buffering
Alkalinity monitoring and dosing capacity sized to the nitrification rate.
Monitoring
Daily nitrite logging during start-up and after every loading change.
Run the numbers
Planning-level estimates to structure the review. Results are approximate and must be confirmed by a qualified aquaculture engineer.
Biofilter Sizing Calculator
Biofilter capacity in a RAS is driven by daily feed load and the ammonia produced per kg of feed (~30 g TAN / kg feed at 45% protein). Media volume is sized to the nitrification rate of the chosen biomedia (typically 0.3–0.7 g TAN / m² / day, or 150–400 g TAN / m³ media / day for K1/K3).
Estimates Only: This calculator is provided for general informational purposes only. Results are approximate and may contain errors, omissions, or outdated information. They do not constitute legal, financial, engineering, tax, technical, or professional advice. Users are solely responsible for independently verifying all calculations, specifications, prices, regulations, and requirements with qualified professionals before making any decisions. By using this calculator, you acknowledge that the website owners, operators, and affiliates accept no responsibility or liability for any loss, damage, or decisions resulting from its use.
Water Exchange Calculator
Daily water exchange controls waste dilution, nitrogen load and overall water-quality stability. Recirculating aquaculture (RAS) turns the full system volume over 4–24 times per day through mechanical and biological water treatment; earthen ponds exchange 5–20% per day; shrimp biofloc systems often run near zero exchange.
Estimates Only: This calculator is provided for general informational purposes only. Results are approximate and may contain errors, omissions, or outdated information. They do not constitute legal, financial, engineering, tax, technical, or professional advice. Users are solely responsible for independently verifying all calculations, specifications, prices, regulations, and requirements with qualified professionals before making any decisions. By using this calculator, you acknowledge that the website owners, operators, and affiliates accept no responsibility or liability for any loss, damage, or decisions resulting from its use.
Stocking Density Calculator
Stocking density (kg per m³ of water) is the single biggest driver of oxygen risk, disease pressure and water-treatment load. RAS tolerates the highest density; ponds and cages the lowest. Overstocking crashes dissolved oxygen before it shows in growth data.
Estimates Only: This calculator is provided for general informational purposes only. Results are approximate and may contain errors, omissions, or outdated information. They do not constitute legal, financial, engineering, tax, technical, or professional advice. Users are solely responsible for independently verifying all calculations, specifications, prices, regulations, and requirements with qualified professionals before making any decisions. By using this calculator, you acknowledge that the website owners, operators, and affiliates accept no responsibility or liability for any loss, damage, or decisions resulting from its use.
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