Reef tank troubleshooting
Diagnose by symptom. Each page lists causes in order of how often they actually happen, with a quick diagnostic and a real fix for each.
All troubleshooting topics
- Cloudy aquarium water — causes and fixesSymptom: The water is cloudy / hazy / milky / green / discolored.
- High nitrate (NO₃⁻) in a reef tank — diagnosis and fixesSymptom: Nitrate reading >20 ppm in a reef tank. Brown algae, hair algae, or dinoflagellate blooms. Cyano spots.
- Low alkalinity in a reef tank — diagnosis and fixesSymptom: Alkalinity below 7 dKH. SPS tips losing color (often the first sign). pH unstable. Calcium also dropping.
- Reef tank algae identification — what is this and how do I fix it?Symptom: Something green/brown/red is growing in your tank that you don't want.
- Coral bleaching — causes and recovery in a home reefSymptom: Coral has lost color — paled, gone white, or its tissue has receded.
- Reef tank pH swings — diagnosis and fixesSymptom: pH below 7.9, above 8.4, or swings more than 0.3 units day to night.
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