Acropora yongei

Acropora yongei builds open, staghorn-like bushes of long, cylindrical branches reaching upward from a common base. Its best-known form in the hobby is the bright green "Green Slimer" with whitish growth tips.

Among Acropora it stands out for its hardiness and fast growth, which is why it is often recommended as a first Acropora. Still, it needs a mature aquarium with stable KH and does not succeed in newly set-up systems.

Trade in stony corals is subject to CITES Appendix II. Because the Green Slimer has been propagated in aquariums for many years, it is easy to find as a frag; choose one instead of a wild-collected colony.

• Green Slimer (Bali green slimer): Bright green body, whitish tips. Not every coral sold under this name may be A. yongei; other similar-looking Acropora species are sold under the same name.
• Purple-tipped yongei: Forms with purple growth tips on a green body are also being propagated.

It lives in the Indo-Pacific, especially around Indonesia and Australia, on reef slopes and in lagoons. In the wild its upright-branched bushes can cover large areas on slopes with steady flow.

• Light: High light; roughly 250–400 PAR. The green color becomes brighter under strong light; a new frag should be acclimated to the light over two to three weeks.
• Flow: Strong, random flow. In weak flow the branches grow thin and long and break easily.
• Placement: The upper part of the rockwork; leave room for the branches to grow 20–30 cm upward. Large colonies can block the light above them, so pruning will be needed later.
• Water parameters: Salinity 1.025–1.026, temperature 25–26.5°C. KH 7–9 dKH with daily swings 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; most of its energy comes from the zooxanthellae algae in its tissue. Very fine powdered food or rotifers can be given once or twice a week. Fast-growing colonies consume a lot of calcium and KH; adjust dosing with regular testing.

It is not aggressive, but its fast-growing branches shade the corals below and can touch those beside it. Keep it 10–15 cm away from LPS and soft corals.

Dwarf angelfish may pick at the polyps. Acropora-eating flatworms (AEFW) and red bugs affect this species too; put newly arrived pieces through a coral dip. Acropora crabs (Tetralia) are harmless.

It is one of the easiest Acropora to propagate. Branch tips of 3–5 cm are cut and attached to a frag plug with gel glue or wedged into a crevice in the rock. The cut tips heal within a few days; regular pruning also opens up the inside of the mother colony.

• Rapid tissue necrosis (RTN): Can occur after a sudden change in KH or temperature; cut off and save the healthy branch tips.
• Tissue loss from the base (STN): As the colony becomes denser, the inner branches are left in shade; prevent this with pruning and strong flow.
• Fading or browning: Whitening indicates too much or too sudden light; browning indicates a lack of light or high nutrients.
• Pests: Crescent-shaped bite marks and brown egg clusters are signs of AEFW; repeat the dip every 10–14 days, at least three times.