Acropora tenuis

Acropora tenuis builds colonies shaped like a bush, with short, upright branches rising from a common base, and like a low table that spreads sideways as it grows. The radial corallites on the branches are tubular and their mouths flare outward like a bowl, giving the coral a texture that resembles a bouquet of flowers. In the trade there are many named forms with different combinations of green, blue, purple and red tones.

Its care carries the general difficulty of the genus Acropora: it needs a mature aquarium, strong light and, above all, stable water chemistry. Newly placed pieces may not show noticeable growth for the first three to six months; frequently changing the lighting and position during this period delays acclimation.

The trade in stony corals is subject to CITES Appendix II. Almost all of the famous color forms are aquacultured frags; choose these instead of a wild-collected colony.

• Walt Disney (Walt Disney acro): A famous clone recognized by its green base, reddish corallites and blue growth tips. It is reported to turn pink under very strong light.
• Other named clones: There are many tenuis forms sold under names given by the sellers themselves; the names describe the color combination and are not separate species.

It lives on the reef crests and clear-water upper slopes of the Indo-Pacific. In these zones the light is very strong and waves and currents are constant. Colonies growing side by side form broad carpets on shallow reefs.

• Light: High light; about 250–400 PAR. A new frag should first be kept under lower light and moved up over three to four weeks. A sudden increase in PAR causes whitening at the tips.
• Flow: Strong, random flow. No detritus should remain between the branches, but a fixed pump outlet erodes the tissue.
• Placement: The upper part of the rockwork, on a ledge that allows horizontal spreading. As the colony becomes denser, thinning out the inner branches keeps the base from being shaded and dying.
• Water parameters: Salinity 1.025–1.026, temperature 25–26.5°C. KH 7–9 dKH with daily change below 0.5 dKH; calcium 400–450 mg/L; magnesium 1300–1400 mg/L. Nitrate 2–10 mg/L, phosphate 0.02–0.08 mg/L.

It is photosynthetic; its zooxanthellae cover most of its energy needs. Very fine powdered food or phytoplankton can be given once or twice a week. Complete depletion of nutrients fades the color and stops growth; overfeeding, on the other hand, brings algae and browning.

It does not attack its neighbors; on the other hand, it is easily burned and shaded. Keep it at least 10–15 cm away from LPS, soft corals and fast-spreading Montipora plates.

Dwarf angelfish may pick at the polyps. The Acropora-eating flatworm (AEFW) and red bugs are the most important pests; put every newly arrived Acropora through a coral dip and, if possible, watch it in quarantine for a few weeks. The Acropora crabs (Tetralia) that live among the branches are harmless.

Branch tips 2–3 cm long are cut and attached to frag plugs with gel glue. In table-shaped colonies, cutting the branches at the edge both yields frags and shapes the colony. The frags are grown on a rack with good flow and lighting close to that of the mother colony.

• Rapid tissue necrosis (RTN): Usually starts after a sudden change in KH or temperature. Immediately cut off the healthy part and save it as a separate frag.
• Slow tissue necrosis (STN): The tissue recedes upward from the base; depleted nutrients, weak flow and a shaded base are the main causes.
• Bite marks and brown egg clusters: A sign of AEFW. Scrape off the eggs and repeat the dip every 10–14 days, at least three times.
• Polyps not extending and fading: Check for red bugs; medication is harmful to shrimp and crabs, so it is applied in a separate tank.