Advanced SPS Coral Care Guide — Growing Acropora & Montipora

SPS (Small Polyp Stony) corals represent the pinnacle of reef aquarium keeping. Demanding in their requirements yet extraordinary in their rewards, genera like Acropora and Montipora can transform a reef tank into a living mosaic of color and movement. This guide covers everything you need to know to keep SPS corals thriving long-term.

Essential Water Parameters for SPS

SPS corals are unforgiving of instability. Their calcium carbonate skeletons require a precise ionic balance maintained consistently — not just on test day, but every single day.

• KH (Carbonate Hardness): 7–9 dKH. Daily swings greater than 0.5 dKH can trigger stress responses or bleaching.
• Calcium: 400–450 ppm. Calcium and KH must remain in balance; elevating one without the other disrupts precipitation chemistry.
• Magnesium: 1,250–1,350 ppm. Magnesium stabilizes calcium and alkalinity in solution. Low magnesium causes both to crash despite dosing.
• Phosphate: Below 0.03 ppm. Elevated phosphate inhibits calcification and suppresses color expression.
• Nitrate: 1–5 ppm. The common mistake is chasing zero nitrate — SPS need trace organics for zooxanthellae function. Completely sterile water produces pale, struggling corals.
• Salinity: 1.025–1.026 specific gravity (35–36 ppt).

The relationship between KH, calcium, and magnesium forms a chemical triangle. Test all three weekly, and when one drifts, check the others before dosing. A two-part dosing system or calcium reactor is strongly recommended for established SPS-dominant tanks — manual top-off dosing rarely maintains the consistency these corals demand.

Lighting: Intensity, Spectrum, and Acclimation

SPS corals require high-intensity lighting, but spectrum matters as much as raw output.

• Target PAR: 200–350 µmol/m²/s depending on species. Acropora millepora and other high-light species can handle 300+, while Montipora capricornis thrives closer to 150–200.
• Spectrum: Emphasize blue wavelengths (420–460 nm). Blue light stimulates fluorescent protein expression — the mechanism behind the vivid purples, greens, and pinks that make SPS so desirable. A high blue-to-white ratio (roughly 70/30) is standard practice.
• Photoperiod: 8–10 hours with a gradual ramp-up mimicking sunrise. Abrupt full-intensity starts stress corals unnecessarily.
• Reliable fixtures: Radion XR30 Pro, AI Hydra 64 HD, and Kessil A360X are proven performers. Avoid cheap single-spectrum fixtures — SPS response to poor spectrum is immediate and visible.

Light acclimation is non-negotiable. When introducing new SPS, place them at the sandbed regardless of their intended final position. Raise them incrementally over 2–4 weeks. RTN (Rapid Tissue Necrosis) and bleaching are commonly caused by light shock, not water quality — especially with frags from dimly lit holding systems.

Water Flow: Random, Strong, and Non-Abrasive

Acropora in the wild lives on reef crests where surge and wave action create turbulent, multi-directional flow. Recreating this in captivity is essential.

• Total turnover: 30–50x tank volume per hour. A 100-gallon system needs 3,000–5,000 gph of total circulation.
• Pump placement: Use two or more circulation pumps positioned at opposing angles. This creates random interference patterns rather than laminar flow, which causes dead spots and STN (Slow Tissue Necrosis) on shaded coral faces.
• Avoid direct blasting: Point pumps at rockwork or glass, not directly at coral tissue. Strong direct flow shreds polyps and inhibits feeding. The goal is turbulent ambient flow, not a jet stream.

Montipora, being a plating or encrusting coral, is somewhat more tolerant of moderate flow, but still appreciates good circulation to remove detritus that would otherwise smother its tissue.

Color Enhancement Strategies

SPS color is a product of both genetics and husbandry. You cannot turn a brown coral vivid purple, but you can absolutely maximize the expression of whatever color potential a coral carries.

• Maintain nitrates in the 2–5 ppm range. Both zero and elevated nitrate suppress fluorescence. The sweet spot varies by coral — experiment carefully.
• Amino acid supplements (e.g., Acropower, Reef Energy Plus) provide organic building blocks that support fluorescent protein synthesis and tissue health. Dose conservatively to avoid nutrient spikes.
• Blue-dominant lighting directly stimulates fluorescent protein production. If colors are dull despite good parameters, increasing the blue ratio is the first adjustment to try.
• Temperature stability at 25–26°C prevents thermal stress bleaching. A dedicated temperature controller and backup chiller are worthwhile investments in warmer climates.
• Avoid large water changes that shift parameters rapidly. Partial changes of 10–15% weekly are preferable to 30% monthly.

Acropora vs. Montipora: Key Differences

While both are SPS, they differ meaningfully in care requirements:

Acropora grows in branching, tabletop, or staghorn forms. It is the more demanding of the two — highly sensitive to parameter swings, requires more intense light, and is susceptible to Acropora-Eating Flatworms (AEFW) and bacterial infections. Tissue loss from the base is a warning sign requiring immediate investigation.

Montipora grows as encrusting plates or capricorn whorls. It tolerates slightly lower light and flow, making it an excellent entry point into SPS keeping. Montipora Eating Nudibranchs (MENs) are a specific pest to watch for — small white specks on tissue are the first visible sign.

Sourcing Quality SPS

The single most important purchasing decision is buying from a keeper who can tell you the parent colony's history, growth conditions, and acclimation status. Frags from a system with parameters close to your own transition far more smoothly than wild-caught or commercially propagated specimens kept under different conditions. Direct breeder sales allow you to ask exactly those questions — and to see the parent colony for yourself.