Physogyra

Physogyra is a species that resembles the bubble coral (Plerogyra), but its bubbles are smaller and denser. During the day the whole colony is covered with bubbles like small grapes, sometimes forked; the bubbles deflate when touched. The tentacles open only at night. The color is usually pale gray or dull green. Its trade is subject to CITES Appendix II; if possible, choose an aquacultured frag instead of a wild-collected colony.

• Light: Low to moderate, about 50–120 PAR; in the wild it lives in shaded crevices.
• Flow: Low and indirect; if the bubbles are placed near a pump they tear.
• Placement: The lower zone of the rockwork or beneath a shaded ledge.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L; nitrate 2–10 mg/L.

It is photosynthetic. Feeding mysis or fine-grained LPS food once or twice a week, in the evening when the tentacles open, helps keep the tissue full.

The tentacles that open at night sting and burn any coral they touch; the bubbles that inflate during the day also shade its neighbor. Leave at least 10–15 cm of space around it. Hermit crabs and some angelfish can damage the bubbles; torn tissue becomes vulnerable to brown jelly.