Why Is My Coral Turning Brown?
Quick Answer
Corals turn brown when zooxanthellae algae overgrow due to excess nutrients, insufficient light, or stress - reducing their vibrant colors.
Coral browning happens when zooxanthellae - the symbiotic algae living inside coral tissue - overpopulate or darken in color. While some browning is normal, significant color loss usually signals a problem that needs addressing.
Common Causes of Brown Coral
1. Excess Nutrients
High nitrates and phosphates cause zooxanthellae populations to explode. More algae means more brown pigmentation that masks the coral's natural colors.
- Test nitrates and phosphates - aim for NO3 under 20ppm, PO4 under 0.1ppm
- Increase water changes if levels are elevated
- Consider adding a refugium or GFO reactor
2. Insufficient Light
Corals compensate for low light by producing more zooxanthellae. The extra algae darkens their appearance.
- Check PAR levels at coral placement - most corals need 75-250 PAR
- Clean salt creep and algae from light fixtures
- Consider upgrading lighting or raising intensity gradually
3. Stress Response
Various stressors can trigger browning as corals prioritize survival over appearance:
- Temperature swings or consistently out-of-range temps
- pH fluctuations
- Recent relocation or fragging
- Chemical contamination
4. Wrong Spectrum
Light spectrum affects color perception and coral pigment production. Too much warm/white light can wash out colors and encourage browning.
How to Restore Coral Color
- Test water parameters - Use the ReefBay app to track NO3, PO4, alkalinity, and calcium
- Reduce feeding if nutrients are high - less food means less waste
- Increase light gradually - 10% intensity increase per week
- Add blue spectrum - Blue light enhances fluorescent proteins
- Be patient - Color recovery takes 2-8 weeks
When Browning Is Normal
Some browning is expected after shipping stress or adding new corals. Give them 2-4 weeks to acclimate before troubleshooting. Also, some coral morphs are naturally brown - they're healthy, just not as colorful.
Track your parameters consistently with the ReefBay app to catch problems early and monitor recovery progress.
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