Feeding the Colony

Corals are animals, and animals eat. But the feeding question is more nuanced than the fish version, because most corals get the majority of their energy from the light-fed algae in their tissue, not from food you add. Feeding is a supplement that accelerates growth and deepens color in the corals that want it — and a source of pollution that fuels algae if you overdo it in the corals that do not.

This chapter sorts out which corals actually benefit from feeding, how to deliver food to them specifically, and how to feed without wrecking your water.

Which Corals Actually Eat

Start by matching effort to reward. Corals fall roughly into three feeding tiers.

Heavy feeders that clearly benefit. Large-polyp stony corals with big fleshy polyps and feeding tentacles — acans, Duncans, open brains, plate corals, blastomussa, chalices — capture and digest meaty food readily, and a fed one grows and colors up noticeably faster than a starved one. These are the corals where feeding pays off most visibly.

Light feeders that take a little. Many zoanthids, some mushrooms, and Euphyllia like hammers and torches will accept fine foods and benefit modestly, though they get most of their energy from light. Feed them opportunistically, not religiously.

Corals that barely bother. Most soft corals, GSP, and to a large extent SPS rely overwhelmingly on photosynthesis and absorbed nutrients rather than captured particles. SPS do take tiny planktonic foods and dissolved nutrients, but you feed an SPS tank mostly by keeping light, flow, and low background nutrients right, not by target-feeding polyps.

Knowing the tiers keeps you from the beginner error of dumping food at corals that will not eat it, which just pollutes the tank.

Reading the Feeding Response

A coral that wants to eat tells you. When food hits the water, feeding corals extend tentacles, become sticky, and slowly draw captured particles toward a central mouth over minutes. An LPS may inflate feeder tentacles it never shows during the day. Watching this response teaches you which of your corals are worth feeding and how much they will actually take before they stop responding. If a coral shows no feeding response after several tries, stop offering — you are feeding the algae, not the coral.

Target Feeding Versus Broadcast Feeding

There are two ways to deliver food, and the right choice depends on the coral.

Target feeding delivers food directly to a specific coral, usually with a feeding tool — a long pipette or baster — that places a small amount of food right onto the polyps. It is precise, efficient, and the least polluting method because the food goes into the coral rather than into the water column. For heavy-feeding LPS, target feeding is the gold standard: turn down the flow for a few minutes so the food does not blow away, place a small portion on each hungry coral, and let it eat.

Broadcast feeding disperses fine food throughout the water for corals to catch passively. It suits tanks with many small-polyp or filter-feeding corals, and it is how you feed corals that eat tiny particles. The downside is efficiency: much of the food never reaches a coral and becomes nutrient load, so broadcast feeding demands more attention to export.

A practical routine for a mixed reef: broadcast a small amount of fine food for the tank generally a couple of times a week, and target-feed the few heavy LPS individually with meatier foods on top of that.

What to Feed

Corals eat a range of foods by size. Heavy LPS take meaty foods like mysis and finely chopped seafood. Smaller-polyp corals take fine particulate foods, powdered coral foods, and rotifers. Many keepers also dose amino acids, which corals absorb directly from the water and which can support growth and color, though they are a supplement, not a staple. The honest truth is that a reef with healthy fish being fed will already have plenty of dissolved and particulate food in the water from fish waste and leftover food — in many tanks the corals are fed indirectly just by feeding the fish well.

The Nutrient Tightrope

Here is the tension at the heart of coral feeding. Corals want some nutrients — nitrate and phosphate at low but non-zero levels feed the zooxanthellae and support color. But feed too heavily and those same nutrients climb, fueling nuisance algae, cyanobacteria, and dinoflagellates, and eventually browning your corals as excess nutrients overload their algae.

The answer is not to feed less; it is to feed and export in balance. Every bit of food you add is nutrient you must eventually remove, and the primary export tool is a protein skimmer, which physically strips dissolved organics out before they break down into nitrate and phosphate. A well-sized protein skimmer is what lets you feed generously — feeding the corals you want to feed — without the nutrient spike punishing you two weeks later. Skimming, water changes, and media form your export side; feeding forms your input side; and you keep them roughly matched.

The only way to know whether they are matched is to test. Feeding blind is how tanks slide into algae. A reef master test kit that reads nitrate and phosphate turns feeding from guesswork into a controlled dial: if you increase feeding and nutrients climb, you increase export; if nutrients bottom out near zero and corals pale, you ease off export or feed a touch more. This balance ties directly into the nutrient chemistry covered in the reef chemistry handbook, but the coral-keeper's version is simple: feed the corals that eat, export what you add, and test to keep the two in balance.

A Sane Feeding Routine

For a typical mixed reef: feed your fish well daily, which feeds the corals indirectly. Broadcast a small amount of fine coral food two or three times a week. Target-feed your heavy LPS individually once or twice a week, cutting flow briefly so the food lands. Watch nutrients on a test kit and adjust export to hold nitrate and phosphate low but not zero. That is the whole discipline. The corals that grow fastest under this routine are exactly the LPS you will soon be fragging to expand your collection.

Feeding Frequency and Restraint

How often to feed corals is less about a fixed schedule and more about restraint. A few target feeds a week for your heavy LPS, plus light broadcast feeding, is plenty for a mixed reef. There is no prize for feeding more, and overfeeding is far more common and far more damaging than underfeeding, because the excess becomes algae fuel long before it becomes coral growth.

Feed in the evening or after lights-out for corals that extend feeding tentacles at night, when they are naturally hunting. Cut the flow briefly so the food lands rather than scattering across the tank. And always feed less than you think you should the first few times, watching how much the corals actually capture before the rest drifts off to pollute the water. You can always add more; you cannot un-pollute a tank. Restraint, here as everywhere in reefkeeping, is the advanced technique that looks like doing nothing.

FAQ

Do corals need to be fed, or is light enough?

For most corals, light is the primary food source through their internal algae, and many soft corals and SPS need no direct feeding at all. But heavy-feeding LPS like acans, Duncans, and open brains grow and color up noticeably faster when target-fed meaty foods. Feeding is a growth-and-color supplement for the corals that want it, not a survival requirement for most.

How do I feed corals without causing an algae outbreak?

Balance input with export. Feed the corals that actually eat, ideally by target feeding so food reaches the coral rather than the water, and match that input with nutrient export — a protein skimmer, water changes, and media. Then test nitrate and phosphate regularly. If feeding pushes nutrients up, increase export; the goal is low but non-zero nutrients, not zero and not high.

What is the difference between target and broadcast feeding?

Target feeding places food directly on a specific coral's polyps with a pipette or baster, which is precise and low-pollution and ideal for heavy LPS. Broadcast feeding disperses fine food throughout the water for corals to catch passively, which suits many small-polyp corals but wastes more food as nutrient load. Most mixed reefs use a little of both: broadcast lightly, target-feed the hungry LPS.