How to feed Corals in a Reef Aquarium
Feeding the corals in our reef aquariums is both an art and a science. Marine biologists study corals in their natural environment, under “perfect” conditions. We use their research findings to provide our reef tanks with the best possible conditions. We have come a long way in learning how to care for our corals. In the early days of reef keeping, some critics said we were simply robbing the reefs for our hobby. Today reef aquarists are farming corals, even helping to restore damaged reefs with our cultured inverts! You probably don’t have a coral farm, but you want your reef to grow and maybe even frag some for your friends. Growth takes energy. Energy comes from food. Let’s explore what nutrition corals need and how to feed them.
Even Photosynthetic Corals Need Food
Photosynthetic corals contain live algae in their tissue. The algae in the coral tissue harvest energy from light and produce nutrients that are absorbed by the corals. These Zooxanthellae (zo-zan-THEL-ee) algae provide a portion of the energy the coral needs to survive. Even photosynthetic corals need more energy, however, than the algae can provide. Studies show that coral needs extra food sources to form new tissue, repair damaged tissue, and for sexual reproduction. Coral polyps will capture free-floating plankton, fish eggs, algae cells… almost anything they can grab with their tentacles. Corals also send out sticky mucus nets. These nets capture bacteria and fragmented pieces of organic debris, which are taken in and digested. The third method of feeding is the absorption of dissolved organic compounds from the water, as well as trace elements, calcium, and magnesium.
While photosynthesis supplies much of a coral’s basic energy needs, it cannot provide all the nutrients required for optimal health. Certain metabolic processes—such as tissue growth, repair, reproduction, and pigment synthesis—require amino acids, fatty acids, and other organic compounds that are not fully produced by zooxanthellae. Heterotrophic feeding (capturing and digesting external food sources) supplies these essential nutrients. In captivity, the need for supplemental feeding is often greater than in the wild, due to lower natural plankton levels and differences in artificial lighting spectra. Insufficient feeding can result in poor growth, pale coloration, reduced polyp extension, and even tissue recession. Recognizing these signs helps aquarists adjust their feeding practices to support vibrant, healthy corals.
Marine biologists discovered that hermatypic corals get about 60% of their energy from the algae (photosynthesis), 20% from capturing floating foods, and 20% from adsorbing dissolved organic compounds. Ahermatypic corals do not contain live algae in their tissues. All of their nutrition must be captured by the polyps, mucus, and adsorbed from the water. These corals include tree corals and gorgonians. These corals are very difficult for most reef aquarists to keep alive. It may be due to the difficult feeding requirements of these species.
What to feed Your Corals
On the reef, corals feed on microscopic crustaceans, called zooplankton.
image by Lycaon
These tiny shrimp-like creatures provide the extra nutrition and energy corals need to grow and reproduce. Zoos, public aquariums, laboratories, and super-serious reef aquarists will raise live zooplankton to feed to their corals. This usually requires growing algae to feed to the zooplankton, before feeding them to the corals. It can get quite complicated for the average reef keeper. A simpler way is to hatch brine shrimp at home. A web search will list the steps necessary to hatch brine shrimp eggs. The baby brine shrimp are easily siphoned out and “squirted” into the reef tank or directly onto the corals. Another method is to place a small piece of shrimp or other meaty food directly on the coral polyps. The polyp will extend their tentacles, grab the food, and pull it into its mouth. Corals can sense or “taste” food that is nearby. Many of the liquid and powder reef foods will stimulate corals to open their polyps and extend their tentacles in a feeding response. Prepared coral foods contain proprietary formulas but we know that many contain essential vitamins, amino acids, trace elements, algae, and zooplankton. Some more complex formulas contain oyster eggs and a variety of whole zooplankton like copepods, rotifers, and brine shrimp.
Matching Food Type and Size to Coral Species
Not all corals feed in the same way or require the same food particle size. Selecting the right food for your corals improves feeding efficiency and reduces waste. Here’s a practical guide:
- Large-Polyp Stony (LPS) Corals (e.g., Euphyllia, Acanthastrea): Prefer larger meaty foods such as mysis shrimp, chopped seafood, or large zooplankton. Target feeding is often effective.
- Small-Polyp Stony (SPS) Corals (e.g., Acropora, Montipora): Feed best on fine particulate foods like rotifers, marine snow, or specially formulated SPS powders. They may also absorb dissolved organic matter.
- Soft Corals (e.g., leather corals, zoanthids): Generally take up dissolved nutrients and benefit from small particle foods or phytoplankton. Some may accept fine zooplankton.
- Non-photosynthetic corals (e.g., gorgonians, sun corals): Require frequent feedings of appropriately sized zooplankton or finely chopped meaty foods.
Signs that food is too large or inappropriate include food drifting away uneaten, lack of polyp extension, or visible rejection of food particles. Avoid foods with excessive fillers, as these can degrade water quality without benefiting your corals.
Feeding Methods and Supplementation
Targeted feeding, with a long feeding tube placed near the polyps, is probably the most popular feeding technique today. Rather than pour a lot of food and nutrients into the water, target feeding places a small amount of food right at the mouth of the corals. This technique greatly reduces the amount of food missing the corals and polluting the water. Many reef keepers add inorganic nutrients to the water, in the form of calcium, magnesium, iodine, and strontium supplements. These essential elements are used by the corals in building their skeleton and new tissues.
Caution with Supplements: Overuse of supplements can lead to nutrient imbalances or even toxicity. Always test your water parameters before adding trace elements or minerals, and remember that not all corals require the same supplementation. More is not always better—excessive supplementation can harm your corals and other tank inhabitants.
When to Feed Your Corals
Night-time is when the action starts on the reef. Zooplankton come out of hiding and start swimming around the coral heads. Currents keep the live food suspended, allowing the coral tentacles to capture it. Ideally, you should feed your corals in the evenings, under low light conditions. Many aquarists turn down the circulation pumps so the food does not get washed away from the corals. Research has shown that corals respond to food with the lights turned on too. It is fun to feed in the light and under darkness, observing the interesting feeding behaviors of each type of coral.
Managing Water Flow During Feeding: If you turn off your pumps to keep food near the corals, be cautious not to leave them off for more than 10–20 minutes. Extended periods without circulation can reduce oxygen levels, create dead spots, and allow food to settle and decay, potentially harming corals and other livestock. Many modern pumps offer a “feed mode” that temporarily reduces flow for a set period, automatically resuming normal circulation. Alternatively, consider leaving some flow on to maintain oxygenation and gently distribute food without washing it away too quickly. Always remember to turn your pumps back on after feeding time is over!
You will likely see, however, that the corals in your tank will adapt to YOUR SCHEDULE. Once they get a taste for feeding in the tank, they can detect traces of food in the water and will usually open up and let you know they are ready, when it is feeding time.
How Much Should I Feed My Corals?
How much to feed is the “art” part of reef keeping. Too much food will simply go to waste. It is possible to over-feed the aquarium and stimulate algal blooms and nitrate spikes. Some aquarists feed once a month, others every day. The best approach is to carefully feed small amounts once or twice a week and see how the corals respond over several weeks. Part of the fun of reef keeping is discovering how your corals respond to your care. Take it slow and you’ll soon know what foods to use and how often to feed your reef.
Adjusting Feeding Based on Tank Feedback:
- Signs of Overfeeding: Increased algae growth, cloudy water, elevated nitrate or phosphate levels, uneaten food accumulating on the substrate, or declining water clarity.
- Signs of Underfeeding: Poor coral polyp extension, pale or faded coloration, slow or halted growth, tissue recession, or lack of feeding response.
Monitor your tank parameters and observe coral behavior regularly. Adjust feeding frequency and quantity gradually, allowing time to see how your corals and water quality respond. Patience and observation are key to finding the right balance for your unique reef system.