The reef-keeping hobby has a feeding problem, and it is not the one most beginners think it is. The beginner thinks the problem is that the corals are not getting enough food. The actual problem is that the beginner is feeding the tank instead of the corals. The food that goes into the water column without being captured by a coral is pollution. It feeds the algae, the bacteria, the nutrient cycle, and eventually the cyanobacteria outbreak. The food that goes directly into a coral polyp is nutrition. The difference between a thriving reef and a struggling one is not how much food the hobbyist puts in. It is how much of that food the corals actually capture.
This article is the working reefkeeper's view of coral nutrition. We will go through the difference between LPS (large polyp stony) corals and SPS (small polyp stony) corals, what each group actually captures and digests, the role of photosynthesis via zooxanthellae, the role of broadcast feeding and target feeding, the foods that work, the foods that pollute, the feeding schedule that produces growth, and the four mistakes I see in the failed reef tanks.
The basic biology
Corals in captivity are animals, not plants, even though they look like plants and are commonly treated as decorations. Each coral is a colony of polyps, each polyp is a soft-bodied animal related to jellyfish and sea anemones, and each polyp has a mouth, tentacles, and a digestive system. Inside the coral tissue are millions of symbiotic algae called zooxanthellae (Symbiodinium species) that photosynthesise and share the sugars they produce with the coral host. The coral also captures planktonic prey from the water column using its tentacles and nematocysts (stinging cells), and digests the prey to obtain proteins, lipids, and other nutrients that the zooxanthellae cannot provide.
The balance between photosynthesis and prey capture varies enormously between coral groups. The LPS corals (Euphyllia, Favia, Acanthastrea, Lobophyllia, Symphyllia, Platygyra, Goniopora, Tubastraea) rely heavily on prey capture. Their polyps are large, their tentacles are well-developed, and they have a strong appetite. The SPS corals (Acropora, Montipora, Pocillopora, Seriatopora, Stylophora) rely heavily on photosynthesis. Their polyps are tiny, their tentacles are short, and they capture very little prey directly. The SPS corals are essentially solar-powered, with a small supplementary diet of dissolved organic matter and the occasional micro-plankton that drifts past.
The practical implication is enormous. The LPS tank is a feeding tank. The SPS tank is a lighting tank. The hobbyist who treats them the same is making a mistake.
What LPS corals actually need
LPS corals need a regular supply of meaty foods. The most commonly used foods are:
- Mysis shrimp. Whole frozen mysis shrimp, thawed in tank water and target-fed to individual corals. The standard LPS food. The mysis is large enough to be captured and digested, and the nutritional profile is good. A medium Euphyllia coral will consume 3 to 5 mysis per feeding, 2 to 3 times per week.
- Brine shrimp (adult, enriched). Less nutritious than mysis, but useful as a treat or as a "training" food to encourage polyp extension in new corals. Enrichment with a HUFA (highly unsaturated fatty acid) product improves the nutritional value.
- Krill (whole, chopped, or paste). Excellent LPS food. The krill is rich in carotenoids, which enhance the coral's colour. Whole frozen krill, chopped, can be target-fed to the larger LPS corals.
- Squid, clam, scallop, fish (raw, chopped). Excellent nutrition but more expensive. Used by serious LPS keepers for show corals.
- Cyclops, rotifers, and other small zooplankton. Useful for small-polyp LPS (Acanthastrea, Micromussa) and for filter-feeding LPS (Tubastraea, which lacks zooxanthellae entirely and is a pure filter feeder).
- Commercial LPS foods. Many brands offer blended frozen or liquid foods designed specifically for LPS. Most are a mix of the above. The quality varies. Some are excellent. Some are mostly water.
The feeding method matters as much as the food. Target feeding (using a pipette or turkey baster to deliver food directly to each coral's mouth or tentacles) is far more efficient than broadcast feeding (just dumping the food into the water). Target feeding delivers the food where it is consumed, with minimal pollution. Broadcast feeding disperses the food into the water, where much of it is captured by the live rock filtration, the protein skimmer, or simply broken down into dissolved nutrients that feed algae.
The typical LPS feeding schedule is 2 to 3 times per week, target-fed. The amount is whatever the corals will consume in 5 to 10 minutes. Overfeeding is a more common problem than underfeeding.
What SPS corals actually need
SPS corals are the opposite extreme. They are primarily photosynthetic and capture very little prey directly. Their nutrition comes from:
- Photosynthesis by zooxanthellae. This is the primary food source. The zooxanthellae convert light energy and CO2 into sugars, which they share with the coral host. The quality and intensity of the lighting directly affects the coral's growth and colour.
- Dissolved organic matter (DOM). SPS corals absorb amino acids, sugars, and other small organic molecules directly from the water column. The water in a mature reef tank is rich in these compounds, produced by the breakdown of fish waste, food residues, and microbial activity.
- Nano-plankton and pico-plankton. Very small organisms (under 200 microns) that the SPS polyps can capture with their short tentacles. These are naturally present in a mature reef tank and are supplemented by some reefkeepers using commercial products (e.g. live phytoplankton, live rotifers).
- Bacterial biomass. The microbial loop in a mature reef tank produces a constant supply of bacteria that the SPS can capture. This is one reason that mature, well-established tanks grow SPS better than new tanks.
The practical implication: SPS corals do not need to be target-fed. The myth that "all corals need to be fed" is wrong for SPS. The lighting, the water quality, and the stability of the system are far more important than the feeding.
SPS keepers who want to supplement the natural production use:
- Oyster eggs, copepods, and other small zooplankton. Delivered via broadcast feeding or dosed into the water column. Some SPS keepers maintain a refugium with chaetomorpha or other macroalgae that produces a constant supply of copepods.
- Live phytoplankton. Dosed into the tank. The phytoplankton is not directly consumed by the SPS but feeds the rotifers and copepods that the SPS can capture. The benefit is indirect.
- Amino acid supplements. Liquid products that provide dissolved amino acids. The benefit is real but small. Overuse leads to nutrient accumulation and algae outbreaks.
The typical SPS feeding schedule is much lighter than LPS. Many SPS keepers feed sparingly, relying on the natural production of the system. The risk of overfeeding SPS is much higher than the risk of underfeeding.
The foods that work and the foods that pollute
Works:
- Target-fed mysis to LPS
- Target-fed krill to LPS
- Frozen blended foods specifically designed for reef tanks
- Live phytoplankton (indirect benefit)
- Live copepods (for SPS and filter feeders)
- Refugium production (natural food for both LPS and SPS)
Pollutes:
- Broadcast feeding of any food (most of it is not captured)
- Overfeeding of any food (the excess feeds algae)
- Foods with high phosphate content (some frozen foods, some flake foods)
- Foods with high nitrate content (some "fish food" blends)
- "Bacterial foods" and other products that boost the bacterial population indiscriminately
- Milk, yeast, and other "homemade" coral foods (these are disasters)
The protein skimmer is the reefkeeper's best friend. It removes the dissolved organic matter that the corals do not consume, before it breaks down into nitrate and phosphate. A well-tuned skimmer is essential for any reef tank, LPS or SPS.
The feeding schedule that produces growth
For an LPS-dominant tank:
- Target feed each LPS coral 2 to 3 times per week
- Vary the food (mysis, krill, mysis-krill blend)
- Feed at lights-out or during a brief dim period, when the corals' tentacles are extended
- Feed only what the corals will consume in 5 to 10 minutes
- Run the protein skimmer heavily for 1 to 2 hours after feeding, then return to normal
- Monitor nitrate and phosphate; if they rise, reduce feeding
For an SPS-dominant tank:
- Light feeding 1 to 2 times per week, or no target feeding at all
- Maintain a refugium with chaetomorpha or other macroalgae
- Dose phytoplankton if desired, but do not overdo
- Keep the lights strong (PAR 250 to 400 for most SPS) and the spectrum appropriate (predominantly blue, with white peaks for growth)
- Monitor for tissue recession, which indicates insufficient light or unstable parameters, not insufficient food
- Keep nitrate below 5 ppm and phosphate below 0.03 ppm for SPS-dominant tanks (LPS can tolerate higher levels)
For a mixed reef:
- Feed the LPS target-fed 2 times per week
- Use broadcast feeding sparingly, only with foods the LPS can capture
- Maintain strong lighting for the SPS
- Use a heavy protein skimmer to remove excess nutrients
- Monitor for nutrient accumulation (rising nitrate, rising phosphate, increasing algae)
The four mistakes
Mistake 1: Broadcast feeding instead of target feeding. This is the most common mistake. The hobbyist dumps a cube of frozen mysis into the tank and watches the fish eat it. The corals do not eat it. The food breaks down into dissolved nutrients that feed the algae. The result is a tank with fat fish and starving corals, plus a slow climb in nitrate and phosphate. The fix: target feed. The food goes where it is consumed. The water stays clean.
Mistake 2: Feeding SPS like LPS. The hobbyist with an SPS-dominant tank reads about target feeding and tries to target feed the SPS. The Acropora polyps are too small to capture the mysis. The food sits on the coral, rots, and produces tissue necrosis. The result is recession and death. The fix: do not target feed SPS. Provide strong lighting and stable water. Let the natural production do the work.
Mistake 3: Overfeeding in a desperate attempt to "fix" a struggling coral. The hobbyist sees a struggling coral, assumes it is starving, and feeds heavily. The overfeeding produces a nutrient spike that triggers a dino outbreak, a cyano outbreak, or an algae plague. The coral does not improve, and now the whole tank is at risk. The fix: a struggling coral is usually a lighting or water quality problem, not a feeding problem. Diagnose correctly before changing the feeding.
Mistake 4: Using foods with hidden phosphate or nitrate. Some "coral foods" and "fish foods" contain significant amounts of phosphate (from the fish or shellfish used in the ingredients) or nitrate (from processing). The hobbyist who feeds heavily with these products is dosing phosphate and nitrate into the tank with every feeding. The result is chronic high phosphate, which feeds hair algae and prevents SPS calcification. The fix: choose foods with low phosphate content, and consider rinsing frozen foods in tank water before feeding to remove some of the phosphate-laden liquid.
Closing the loop
Coral feeding is a system, not a single act. The LPS tank needs regular target feeding with appropriate foods. The SPS tank needs strong lighting and stable water, with light or no target feeding. The mixed reef needs a balance that respects the needs of both groups. The hobbyist who understands the difference, who target feeds instead of broadcast feeding, who does not overfeed, and who chooses low-phosphate foods, will have a thriving reef. The hobbyist who treats all corals the same, who broadcast feeds, who overfeeds, and who ignores the phosphate content of the foods, will have a struggling tank with chronic algae outbreaks. The corals are the same. The difference is the strategy.
