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SPS coral feeding is where reef keeping gets serious. Small polyp stony corals like Acropora, Montipora, Pocillopora, Stylophora are the most visually spectacular animals in the hobby and the most demanding to keep well. Their reputation for difficulty is earned, but it's often attributed to the wrong causes. Most SPS failures aren't lighting failures or flow failures. They're nutritional failures that play out slowly over months, in a tank that looks acceptable right up until something tips.
Understanding what SPS corals actually need to eat, and why getting it right matters more than most guides acknowledge, is the foundation of keeping these animals at their best rather than merely keeping them alive.
- Darren, Reefphyto
What SPS Corals Are Actually Eating
SPS corals have tiny polyps often just millimetres across with correspondingly small feeding apparatus. They can't capture and ingest the larger zooplankton that LPS corals feed on so effectively. What they do instead is absorb nutrition from multiple sources simultaneously: photosynthesis via their zooxanthellae provides the majority of their energy under good lighting; dissolved organic matter and fine particulates are absorbed passively through tissue; and small-particle zooplankton rotifers, copepod nauplii, bacterioplankton are captured actively by their tiny nematocyst-armed polyps.
The practical implication is that SPS coral feeding is less about direct prey delivery and more about maintaining a water column rich enough in fine food particles that passive and active absorption is happening continuously. A single targeted feeding event twice a week is far less useful for SPS than a consistently productive water column that's providing nutrition around the clock. This is a fundamentally different feeding philosophy from LPS keeping, and it's where many reef keepers who transition from LPS to SPS make their first mistake continuing to think about feeding as a discrete event rather than an environmental condition to maintain.
The Role of Zooxanthellae and Its Limits
SPS corals are more photosynthetically dependent than soft corals or LPS species. Under high-quality, high-intensity lighting PAR of 200–400+ µmol/m²/s depending on species and position the zooxanthellae within SPS tissue can provide up to 80–90% of the coral's energy requirements. This is why lighting gets so much attention in SPS keeping, and rightly so.
But the remaining 10–20% of heterotrophic nutrition matters enormously to the quality of the outcome. Research on wild Acropora colonies consistently shows that heterotrophic feeding contributes disproportionately to skeletal growth, tissue quality, and the production of the fluorescent pigments that give SPS corals their most vivid colouration. A coral meeting its energy requirements through photosynthesis alone will survive but it won't achieve the growth rates, tissue density, or colour intensity of the same coral in a nutritionally rich environment.
The other critical factor is that zooxanthellae themselves need nutrients to photosynthesise efficiently. Ultra-low-nutrient systems where nitrate is at near-zero and phosphate is undetectable were fashionable for a period in SPS keeping and produced the characteristic pale, washed-out "stress colouration" that was sometimes marketed as desirable. It isn't. Zooxanthellae require trace nitrogen and phosphorus to function properly. Maintaining very low but non-zero nutrient levels, nitrate 1–5 ppm, phosphate 0.03–0.08 ppm combined with regular plankton additions produces better colouration and healthier tissue than chasing zero.
Phytoplankton and SPS Corals
Live phytoplankton benefits SPS systems less through direct coral consumption the cells are often too small to trigger active capture by SPS polyps and more through what it supports. A regular phytoplankton addition maintains the microbial food web that produces the bacterioplankton and dissolved organics that SPS corals do absorb passively. It feeds the copepod and rotifer populations in the refugium that produce the small-particle zooplankton SPS corals can actively capture. And it contributes to the low-level background nutrients that zooxanthellae need to function.
In an SPS system with a mature, productive refugium, regular phytoplankton dosing into the refugium two to three times weekly underpins the entire live food chain without adding particle waste directly to the display tank. This is the most efficient way to use phytoplankton in an SPS context feeding the system rather than feeding individual corals directly.
Live Zooplankton
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Live Zooplankton | Reefphyto You've added a new coral and watched it stay closed for weeks. Your SPS aren't extending the way they should. Your fish are present and your water is clean, but the tank feels static, like something… read more
Zooplankton: Size Matters for SPS Feeding
For SPS coral feeding specifically, particle size is the determining factor in what gets captured and consumed versus what drifts past uneaten. Rotifers at 50–200 microns are ideally sized for SPS polyps and are the most reliably captured live zooplankton by small-polyp species. Copepod nauplii the larval stage of copepods, smaller than adults are similarly sized and nutritionally dense, and a productive refugium running live copepod cultures produces a continuous supply of nauplii that enter the display tank and provide ongoing SPS nutrition without any direct feeding intervention.
Adult copepods at 500–1,000 microns are too large for most SPS polyps to capture efficiently, but they contribute to the system by producing nauplii and by becoming prey for the fish sharing the SPS display mandarins, small wrasses, and other planktivores that benefit from the same live food infrastructure.
Broadcast additions of live rotifers directly into the display tank two to three times weekly, with wavemakers reduced to minimum flow for 15–20 minutes to allow particles to distribute through the rockwork, is the most effective direct SPS feeding method. The rotifers remain alive and moving in the water column, triggering the nematocyst response in SPS polyps far more reliably than static food particles.
Amino Acids and Prepared Coral Foods
Dissolved amino acid supplements are the most consistently effective prepared food category for SPS coral feeding. Amino acids are absorbed directly through coral tissue, no capture event required and provide the protein building blocks that support tissue growth, wound repair, and the production of fluorescent pigments. Regular amino acid dosing is one of the most reliable ways to improve SPS colouration over a 4–8 week period, and it works synergistically with live plankton rather than competing with it.
Broadcast coral food preparations, fine-particle powdered foods like Reef Roids provide a broader nutritional profile including lipids and vitamins that dissolved amino acids alone don't cover. Used as a broadcast addition two to three times weekly, they complement live food additions rather than replacing them. The key with powdered coral foods in SPS systems is dosing conservatively these products are nutrient-dense and it's easy to tip nitrate and phosphate above the ranges where SPS colouration begins to suffer.
Water Quality, Flow, and the SPS Feeding Environment
SPS coral feeding happens continuously in a healthy system, not just during scheduled feeding events. The water quality conditions that allow this matter as much as what you add to the tank.
High, randomised flow is essential not just for gas exchange and detritus suspension, but because it carries food particles through the coral colonies and past individual polyps. Dead spots in an SPS tank are nutritional dead zones as much as they are detritus accumulation points. Wavemakers set to randomised or wave patterns produce the kind of multidirectional flow that delivers food particles to polyps on all sides of a colony, not just those facing the current.
Protein skimmer management during feeding additions requires attention. A skimmer running at full efficiency will export fine food particles within minutes of them being added to the system. For broadcast food and rotifer additions, turning the skimmer off or to minimum output for 60 minutes post-addition gives particles time to distribute and be absorbed before export. For phytoplankton dosing into the refugium, the display skimmer impact is reduced, another reason the refugium-first approach works well for SPS systems.
Water clarity is also a feeding variable that's often overlooked. Dissolved organic yellowing compounds scatter and absorb light, reducing the effective PAR reaching SPS polyps and thereby reducing their photosynthetic output. Activated carbon run continuously maintains the water clarity that keeps photosynthesis the dominant energy source for SPS operating at full efficiency.
Signs That Your SPS Coral Feeding Is Working
SPS corals don't show the immediate, dramatic feeding responses of LPS there's no tentacle extension, no visible capture event to observe. The signs of good SPS nutrition are slower to appear but unambiguous when you're looking for them. New skeletal growth the white tips on Acropora branches, the expanding edges on Montipora plates is the most reliable indicator that a coral is receiving adequate nutrition alongside good lighting and chemistry. Vivid, saturated pigmentation rather than pale or washed-out tissue indicates zooxanthellae are functioning well and amino acid nutrition is adequate. Dense, plump tissue coverage rather than thin skin over skeleton indicates protein nutrition is sufficient.
If growth has stalled on a coral with stable parameters and good lighting, heterotrophic nutrition is the variable to address first. A consistent two to three week trial of regular live rotifer additions and amino acid dosing is the simplest diagnostic if growth resumes and colouration improves, nutrition was the limiting factor.
A Note from Darren
SPS coral feeding is one of those areas where the reef keeping community spent years making it more complicated than it needs to be chasing ultra-low nutrients, debating coral food brands, and overlooking the fundamental point that these animals evolved in a plankton-rich ocean and need a plankton-rich tank to perform at their best. A productive refugium, regular live rotifer and phytoplankton additions, and conservative amino acid supplementation covers almost everything an SPS system needs nutritionally.
If you're struggling with SPS growth or colouration and want to talk through your system specifically, call us on 01267 611533 or use the contact page. I'm happy to help work through it.
