Pavona cactus

Pavona cactus is a stony coral made up of upright, thin, contorted leaves (fronds). The fronds are at most a few millimeters thick and carry polyps on both faces; together they look like a pile of potato chips or lettuce. In the wild it is mostly olive green and brown; in the aquarium green, cream and light-edged forms are seen.

In the hobby it is counted among the "small-polyp" corals, but it needs far less light than Acropora and is more forgiving. This makes it a suitable SPS option for mixed reef aquariums with moderate light. Its thin fronds are fragile; broken pieces can also become new colonies.

Trade in stony corals is subject to CITES Appendix II. Because it is easily propagated in aquariums, choose a frag instead of a wild-collected colony.

It lives from the Red Sea to the Indo-Pacific in sheltered lagoons, bays and on fringing reefs whose water becomes turbid at times. In these places protected from waves, colonies fusing together can form frond fields spreading over several meters. Such environments explain its preference for moderate light and moderate flow in the aquarium.

• Light: Moderate light; roughly 75–250 PAR. Stronger light brings no benefit and can lead to bleaching. Under low light the fronds flatten and the color darkens.
• Flow: Moderate, random flow. If detritus builds up between the fronds, tissue starts to die from that spot; very harsh flow, on the other hand, tears the thin fronds.
• Placement: The middle part of the rockwork or a solid rock near the sand; leave space around it, since the colony will expand upward and outward.
• Water parameters: Salinity 1.025–1.026, KH 7–9 dKH, calcium 400–450 mg/L, magnesium 1250–1400 mg/L. Nitrate 2–10 mg/L, phosphate 0.02–0.08 mg/L. It is not as sensitive as Acropora, but a sudden KH change causes tissue loss along the frond edges.

It is photosynthetic; it gets most of its energy from the zooxanthellae algae in its tissue. Its polyps are very small, so it cannot capture large foods; phytoplankton or very fine powdered foods make a limited contribution. In a regularly fed aquarium with fish no extra food is needed.

This genus can develop sweeper tentacles over time and sting neighboring corals; there are also observations of chemical competition. For this reason leave at least 10–15 cm between it and neighboring corals. It is itself easily stung by strong LPS such as Euphyllia and Galaxea.

Dwarf angelfish and butterflyfish may pick at the polyps. No common pest specific to this species is known; still, put new pieces through a coral dip.

A 2–4 cm piece is cut from the edge of a frond with sharp cutters and attached to a frag plug with gel glue. The thin tissue tears easily; make a single, clean cut and do not crush it. An iodine-based coral dip after cutting reduces the risk of infection. Pieces that break off and land in the sand can also be grown on by gluing them to a solid rock.

• Tissue loss at the base of the fronds: As the colony grows, it is normal for the lower fronds to get no light or flow; in the wild, too, the lower part of the fronds is dead. If the loss moves upward, increase flow and thin the colony.
• Bleaching: Light that is too strong or increased too suddenly. Move the coral lower.
• Detritus and algae: Detritus collecting between the fronds kills the tissue; change the flow direction and blow the detritus off with a pipette now and then.
• Torn tissue: Avoid handling the fronds during maintenance.