Acropora millepora

Acropora millepora builds colonies of short, dense branches that, seen from above, resemble a round cushion. The surface of the branches is covered with small radial corallites arranged like scales, giving the coral a jagged, textured look. In the trade there are forms in pink-salmon, green, orange and purple tones; in most of them the polyps are a different color from the body.

The name should not be confused: "Millepora" is also the genus name of the fire corals (hydrozoans). In the hobby, "millepora" refers to this Acropora species.

It is considered one of the Acropora that adapt best to the aquarium; even so, it needs an aquarium at least 6–12 months old with settled water parameters and is not suitable as a first experience with stony corals. The trade in stony corals is subject to CITES Appendix II. Wild-collected colonies are much more sensitive to transport and changes in lighting; buy an aquacultured frag or a maricultured colony.

• Color forms: Colonies with green, pink-salmon, orange and purple tips are also seen in the wild.
• Trade names: Selected clones sold under names such as "Sunset Millepora" and "Rainbow Millepora" are also this species; the names vary from seller to seller.

It lives on the shallow reef flats, reef crests and upper slopes of the Indo-Pacific. There is strong sunlight and wave action here; the short, dense branches reduce breakage in this turbulent environment. A study on the Great Barrier Reef found that green fluorescent forms bleached less than other color forms during a hot summer.

• Light: High light; about 250–400 PAR. A new frag should first be placed at around 150–200 PAR and moved to the upper part over three to four weeks.
• Flow: Strong, random flow that changes direction. The branches should sway, but should not sit under the constant blast of a single pump.
• Placement: The upper part of the rockwork, on a solid base; leave space around it because the colony will spread sideways.
• Water parameters: Salinity 1.025–1.026, temperature 25–26.5°C and stable. KH 7–9 dKH, with daily fluctuation 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. Nutrients bottoming out at zero is as harmful as them running high.

It gets most of its energy from the zooxanthellae in its tissue. Very fine powdered coral food, phytoplankton or amino acid supplements can support color and growth, but are not essential. Overfeeding raises nitrate and phosphate and does more harm than good.

It is not aggressive toward its neighbors; on the other hand, it is itself easily harmed. Long-tentacled LPS, corals that extend sweeper tentacles and fast-spreading soft corals burn or shade it; leave at least 10–15 cm of space. Using activated carbon against the chemicals released by leather corals is helpful.

Dwarf angelfish and some butterflyfish may pick at the polyps. Its main pests are the Acropora-eating flatworm (AEFW, Prosthiostomum acroporae) and red bugs (Tegastes acroporanus). The small Acropora crabs (Tetralia) that live among the branches, on the other hand, are harmless.

A branch tip 2–3 cm long is cut with coral shears and attached to a frag plug with gel glue. After cutting, the frag is kept in a spot with good flow and lighting close to that of the mother colony; it attaches to the plug within a few weeks. A coral dip before and after cutting prevents pests from spreading.

• Rapid tissue necrosis (RTN): The tissue peels away along the branch within one or two days. It is usually triggered by a sudden change in KH, temperature or salinity. Immediately cut off the healthy part and save it as a separate frag.
• Slow tissue necrosis (STN): The tissue slowly recedes from the base upward. Nutrients bottoming out at zero, KH swings and weak flow are the main causes.
• Crescent-shaped bite marks: A sign of AEFW; scrape off the brown egg clusters on the bare parts of the skeleton and repeat the dip every 10–14 days, at least three times.
• Yellow-red dots running over the tissue: These are red bugs; polyp extension decreases and the color fades. Medication also kills shrimp and crabs, so treatment must be done in a separate tank.