Coral Nutrition: Feeding a Reef Without Feeding Algae

By now you know most corals feed themselves with light. So why feed them at all? Because “mostly” isn’t “entirely,” and thoughtful feeding can noticeably improve growth and color. The trick is doing it without tipping your clean, low-nutrient water into an algae farm. This lesson is about that balance.

Why this matters for your tank

Feeding sits on a knife’s edge. Underfeed, and corals grow slowly and colors stay muted. Overfeed, and the leftover nutrients spike nitrate and phosphate, feeding exactly the algae you’re trying to avoid (remember: reef water is naturally nutrient-poor, Lesson 1). Getting nutrition right is one of the more satisfying skills to develop because you can see the payoff in your corals.

Core concepts

Two ways corals eat

Corals feed on two channels:

• Autotrophy: the light-powered algae partnership. For most beginner corals, this is the bulk of their diet, which is why lighting (Lesson 6) is the first nutrition lever.
• Heterotrophy: actively capturing or absorbing food from the water: plankton, tiny particles, and dissolved organics.

A well-lit coral can survive on autotrophy alone, but many corals grow faster and color up better with some heterotrophic feeding on top. Think of light as the meal and feeding as the vitamins.

What different corals want

• LPS corals (hammer, torch, acan, candy cane) have larger polyps and tentacles and readily take meaty foods: small bits of mysis or a dedicated coral food placed near the mouth.
• SPS corals feed on much smaller particles: think fine plankton and dissolved nutrients rather than chunks.
• Soft corals mostly rely on light and absorbed nutrients; many need little to no direct feeding.
• Filter feeders (like some non-photosynthetic corals and clams) depend heavily on food in the water: these are advanced and hungry.

Nutrients are a feature and a risk

Everything you feed adds nitrogen and phosphate to the water. A little is essential: a tank scrubbed to zero nutrients often looks pale and “starved,” and corals lose color. But excess is the classic cause of algae and cyano outbreaks. The goal is low but not zero, and stable. Feeding is your main input knob; water changes, skimming and nutrient export are the output knobs. Coral nutrition is really about balancing that in-and-out.

Feed the tank as a system

Note that feeding your fish also feeds your corals and bacteria indirectly: fish waste and food particles become nutrients the whole system uses. So “feeding the reef” isn’t only about squirting food at corals; it’s about the total nutrient budget of the tank.

In your tank

• Start conservative. Feed lightly and observe. It’s far easier to add food than to undo an algae bloom.
• Target feed LPS by gently dispersing a small amount of coral food near them (turn flow down briefly so it doesn’t blow away), a couple of times a week, not daily blasts.
• Watch your nutrients. Test nitrate and phosphate. Creeping algae and climbing numbers mean back off; pale corals and near-zero numbers mean you can feed a touch more.
• Don’t chase zero. A little nutrient is healthy. Stability beats sterility: the recurring theme of this whole course.

You’ve now covered corals from biology to feeding. But a reef tank isn’t only corals: the fish are part of the ecosystem too, and they change how the whole system behaves. Next: fish biology for reefers.