Saltwater Issues
Coral Not Opening
Symptoms
- Polyps stay retracted for days after placement or a parameter change
- Tissue looks healthy but no extension
- Other corals in the same tank are open and feeding normally
Likely causes
- Settling-in period after shipping or a move — totally normal for 3–7 days
- Flow too strong, too weak, or hitting the coral directly
- Lighting too intense for placement, especially under new LEDs
- Pest pressure — flatworms, nudibranchs, or vermetid stings
- Unstable alkalinity or salinity swings
Immediate steps to take
- Leave it alone for 5–7 days unless tissue is visibly receding
- Move it lower and shadier — most corals tolerate a step down better than too much light
- Aim flow across, not directly at, the coral
- Inspect at lights-out with a torch for nocturnal pests
- Test alkalinity, calcium, magnesium, and salinity; correct any drift slowly
Long-term prevention
- Always dip new corals before they enter the display
- Place new frags low and shaded, then move up over weeks
- Hold alkalinity within ±0.5 dKH of your baseline — stability beats perfect numbers
- Avoid stacking new corals near aggressive neighbours
Recommended products & practices
Stability is the single biggest factor for coral health. A reliable test routine (alkalinity weekly, full panel monthly) and gentle, indirect flow solves most non-pest closure issues.