SPS (Acropora etc.)

About SPS (Acropora etc.)

SPS, or Small Polyp Stony corals, is a collective term for hard corals with tiny polyps, with Acropora being the most iconic genus. They are found across shallow tropical and subtropical reefs and are celebrated for the remarkable diversity of their skeletal architectures—branching, tabletop, plating, and encrusting forms among them. Their most striking visual feature is the intense fluorescent coloration—electric blues, vivid greens, deep purples, and fiery oranges—that glows brilliantly under actinic and UV lighting. Because individual specimens vary dramatically in color expression, a collector culture has grown around sourcing rare and unusual morphs. In the aquarium, SPS demand powerful lighting, ultra-low nutrient levels, and unwavering calcium and alkalinity stability; they are among the most parameter-sensitive organisms kept in the hobby. The reward, however, is tangible monthly growth and the eventual development of sweeping colonies that transform a reef tank into a breathtaking living sculpture. For dedicated reef keepers, mastering SPS represents the pinnacle of the craft.

7 things to know before welcoming a SPS (Acropora etc.)

1. 1Intense Light Required

   SPS corals rely heavily on zooxanthellae for energy and require high-intensity, reef-spectrum lighting — typically powerful LEDs. Insufficient light quickly leads to bleaching, making a quality reef-grade fixture a non-negotiable investment.

2. 2Water Stability Is Critical

   Calcium (~420 ppm), alkalinity (8–9 dKH), and magnesium (~1350 ppm) must remain consistently stable. Sudden swings cause polyp retraction; prolonged imbalances lead to bleaching and death.

3. 3Ultralow Nutrients Needed

   Elevated nitrates and phosphates cause zooxanthellae overgrowth, dulling coloration. Target nitrates below 5 ppm and phosphates below 0.05 ppm, typically maintained with a protein skimmer, activated carbon, and phosphate media.

4. 4Strong Flow Is Essential

   Detritus accumulation in branches triggers STN (slow tissue necrosis), so turbulent, multi-directional flow is essential. Multiple wavemakers placed to eliminate dead spots are strongly recommended.

5. 5Act Fast on Bleaching/STN

   STN/RTN (slow/rapid tissue necrosis) can spread from tip or base and kill a colony within days. Promptly frag affected areas, isolate them, and immediately re-evaluate water chemistry, flow, and lighting.

6. 6High Setup and Running Costs

   High-end lights, protein skimmers, wavemakers, and a calcium reactor or two-part dosing system can amount to hundreds of thousands of yen. Electricity costs are also significant — calculate monthly running costs before starting.

7. 7Check Coral Compatibility

   LPS and soft corals can release allelopathic compounds harmful to SPS. Aggressive LPS like Galaxea also have long sweeper tentacles — ensure adequate spacing between corals to prevent chemical and physical damage.

Frequently asked questions about SPS (Acropora etc.)

Q.What is the difference between SPS and LPS corals?

A.SPS refers to hard corals with small polyps and dense calcium carbonate skeletons (e.g., Acropora, Montipora), while LPS describes hard corals with large, fleshy polyps (e.g., Torch, Hammer corals). SPS are generally more sensitive to water quality changes and are considered harder to keep.

Q.What tank size is recommended for SPS?

A.A minimum tank size of 90–120 cm (200 L or more) is generally recommended. Larger water volumes buffer against sudden parameter swings and make stability easier to maintain. Smaller tanks are possible but significantly increase the difficulty of keeping parameters stable.

Q.Can a bleached SPS coral recover?

A.If caught early, bleached SPS can recover once water quality is corrected and light intensity is temporarily reduced, allowing zooxanthellae to re-colonize the tissue. However, if rapid or slow tissue necrosis (RTN/STN) has spread to expose bare skeleton, recovery is unlikely and fragging the remaining healthy tissue is often the best response.

Q.Can SPS be kept with other corals and fish?

A.LPS and soft corals can sting SPS with sweeper tentacles, causing necrosis, so adequate spacing between colonies is essential. Choose fish that do not nip at coral (e.g., gobies, clownfish) and avoid species known to bite skeletal tips or polyps.

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