Galaxea Coral

Galaxea is a stony coral made up of small, star-shaped corallites. Each corallite has sharp, protruding septa; during the day short tentacles, mostly white-tipped, open from these corallites and the colony resembles a starry night sky. The color can be green, gray, brown or reddish.

Do not be fooled by its calm appearance: Galaxea is one of the most aggressive corals kept in aquariums. For this reason it should only be kept in a large aquarium with well-planned placement. Its trade is subject to CITES Appendix II; most of those sold are maricultured or aquacultured, so choose those.

It is common on wave-sheltered reefs from the Red Sea to the Central Pacific and can be one of the dominant species on nearshore reefs. In the wild, colonies can form columns or masses exceeding five meters.

• Light: Moderate, about 100–250 PAR. It also adapts to lower light.
• Flow: Moderate and variable. Detritus should not collect between the corallites.
• Placement: The middle zone of the rockwork, on a ledge far from other corals or on a separate rock. Watch which way the current carries the sweeper tentacles.
• Water parameters: Salinity 1.024–1.026, KH 7–10 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. With stable values it grows fast and its calcium consumption is noticeable. Nitrate 2–10 mg/L and phosphate 0.03–0.1 mg/L are suitable.

It is photosynthetic and gets most of its nutrition from light. It also catches plankton with its tentacles; feeding fine-grained coral food or chopped mysis once or twice a week speeds up growth. Supplemental feeding is not essential.

It is very aggressive. In addition to its normal tentacles, especially at night, it extends stinging "sweeper" tentacles that reach 15 cm and sometimes more; most corals these tentacles touch die. Leave at least 15–20 cm of space in every direction and, in particular, do not place corals downstream of it. When it meets Euphyllia and other aggressive LPS, both sides get hurt.

Dwarf angelfish and butterflyfish may pick at the tentacles. It has no problems with most reef fish and invertebrates.

It is easy to propagate. A piece is snapped off the edge of the colony with coral cutters or cut with a saw and glued to a frag plug. Because the corallites are thin and fragile, touch the tissue as little as possible while cutting. The frags attach and spread quickly.

• Tissue recession: Tissue loss starting at the edges is usually due to KH swings or a change in lighting.
• Burns on neighboring corals: If white, dead patches appear on corals near the Galaxea, increase the distance or make the colony smaller.
• Fading color: Seen after a sudden increase in light; increase the light gradually.