Ultimate Koi Keeping Fish Water Chemistry Guide

Why Water Chemistry Matters in Koi Keeping

• Koi produce a large bioload, meaning they generate significant waste.
• Ponds are closed systems; any waste or chemical imbalance directly affects the inhabitants.
• Poor water quality is responsible for 90% of koi health issues.

Understanding the Aquatic Nitrogen Cycle

• Ammonia (NH3/NH4+): Primary fish waste and decay product. Toxic above 0.02 ppm (NH3).
• Nitrite (NO2-): Formed from ammonia by bacteria. Toxic above 0.5 ppm.
• Nitrate (NO3-): Final byproduct. Aim for <40 ppm; ideal <20 ppm.
• Biofiltration: Bacteria like Nitrosomonas and Nitrospira process these toxins.
• Cycle Time: 4–6 weeks (or 1–2 weeks with seeded media).

pH (Power of Hydrogen)

• Ideal range: 7.0 to 8.5
• pH swings are more dangerous than high or low stable values
• Higher pH increases ammonia toxicity

KH (Carbonate Hardness / Alkalinity)

• Stabilizes pH and prevents crashes
• Ideal range: 100–150 ppm (6–8 dKH)
• Use baking soda to raise KH

GH (General Hardness)

• Reflects calcium and magnesium levels
• Essential for koi development and slime coat health
• Ideal range: 100–200 ppm (6–12 dGH)

Ammonia (NH3/NH4+)

• Extremely toxic — keep at 0 ppm
• NH3 increases with pH and temperature

Nitrite (NO2-)

• Prevents oxygen transport in blood (brown blood disease)
• Use salt (0.1–0.3%) to block nitrite uptake

Nitrate (NO3-)

• Chronic toxin that weakens koi immunity
• Control with water changes, plants, or nitrate media

Dissolved Oxygen (DO)

• Target range: 6–8 ppm
• Essential in summer when warm water holds less oxygen
• Ensure surface agitation with aeration, waterfalls, air stones

Temperature

• Ideal range: 15°C to 25°C (59°F to 77°F)
• Above 28°C: Risk of oxygen stress
• Below 10°C: Reduce or stop feeding

Water Testing & Monitoring

Essential Equipment

• Liquid Test Kits: Accurate and affordable
• Digital Meters: Use for pH, TDS, DO
• Testing Schedule: Daily during cycling, weekly for stable ponds

Logging and Tracking

• Use a physical logbook or spreadsheet
• Watch trends and prevent issues early

Water Quality Management

Water Changes

• Routine: 10–20% weekly
• Match temperature and pH to pond
• Always dechlorinate tap water

Chlorine vs. Chloramine

• Chlorine: Removed by aeration or dechlorinators
• Chloramine: Must be neutralized; releases ammonia

Stabilizing Parameters

• Low KH: Add baking soda
• Low GH: Use mineral additives
• High nitrate: Increase water changes or add plants
• Ammonia/Nitrite: Use binders and boost biofiltration

Useful Pond Additives

Troubleshooting Common Water Issues

Ammonia Spikes

• Stop feeding
• Do 25–50% water change
• Add binder (e.g., Prime)
• Boost filtration with bacteria

pH Swings

• Check and maintain KH
• Avoid massive water changes with mismatched pH
• Use buffers for gradual correction

Crystal Clear Water ≠ Safe Water

• Don’t rely on clarity alone — test frequently

Ideal Water Parameter Cheat Sheet

• pH: 7.0–8.5
• KH: 100–150 ppm
• GH: 100–200 ppm
• Ammonia: 0 ppm
• Nitrite: 0 ppm
• Nitrate: <40 ppm (ideal <20 ppm)
• Dissolved Oxygen: 6–8 ppm
• Temperature: 15°C–25°C