Feeding Soft Corals in a Reef Tank

Soft corals are either non-photosynthetic and must acquire all their food from surrounding saltwater or photosynthetic which obtain their food in many ways. One way is through symbiotic algae (zooxanthellae) living in the tissue of coral polyps. Through photosynthesis, zooxanthellae creates nutrients for itself and its host coral.

Soft corals also obtain food by actively catching and eating zooplankton, phytoplankton, bacterioplankton, etc. Another way corals obtain food is through the absorption of dissolved organic molecules and particulate organic material.

As you can see, photosynthetic corals have an assortment of feeding choices. This has caused much confusion for hobbyist, should they feed their corals or let them survive on good light alone.

There are many reefs with healthy populations of beautiful photosynthetic corals which have never been supplemented with coral foods. Even though the only nutrient supplied by zooxanthellae is carbohydrates which are sugar and starches. But for corals to grow and exist they require vitamins, lipids, proteins, and more. They acquire most of these nutrients through uneaten fish food, fish waste, bacteria, etc.

This leads to the question, will corals thrive or simply survive if they are not fed food they would normally consume in nature?

There are corals like Zoanthids, which grow and multiply in a reef aquarium without additional food, as long as there is a reasonable fish population. On the other hand, there are also photosynthetic corals that do not do well unless they are supplemented with coral food regularly. With this said most corals fed on a regular basis will grow faster and appear healthier than their non-supplemented counterparts.

There is a vast array of corals with diets varying from microscopic algae to corals that eat small fish and chunks of raw seafood. Let’s take a close look at some ideal foods for our coral friends.

Coral Foods

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  • Plankton is a universal name for phytoplankton and zooplankton.
  • Phytoplankton is nutrient-packed microscopic algae. This is not one type of algae but a large group of microalgae made up of dinoflagellates and diatoms. In the ocean, phytoplankton provides food for a wide assortment of sea creatures including clams, feather dusters, corals, zooplankton, and more.
  • Zooplankton is a plethora of microscopic to small aquatic animals. These include animals that will remain zooplankton their entire life (copepods and brine shrimp) as well as animals that are considered zooplankton during only a part of their lives (the larvae stage of most fish, snails, and clams.) Some zooplankton frequently used to feed corals are rotifers, copepods, brine shrimp, and mysis shrimp.
  • Frozen coral foods are readily available from aquarium and pet stores. They include meaty foods like brine shrimp, chopped clams, chopped shrimp, cyclops, krill, mysis shrimp, silversides (small whole fish), rotifers, zooplankton, and more. There are also frozen coral foods which are a blend of phytoplankton and tiny zooplankton. Many of the frozen foods mentioned are also used to feed invertebrates and fish. Some frozen foods are a combination of all kinds of foods in a single package designed to feed corals, fish, and invertebrates. This food blankets the water with an assortment of different-sized particles.
  • Liquid foods include live foods, preserved (once alive), and specialty blends. Live food and most preserved food contain critters like phytoplankton, copepods, oyster eggs, and rotifers. Liquid specialty blends include foods that replicate natural marine snow in the ocean to an assortment of other combinations of food and matter for filter feeders.
  • Dry coral foods include dried phytoplankton, zooplankton, krill, and lots of other seafood. There are also proprietary coral food blends.

What is the best time to feed corals?

In the ocean, corals normally extend their tentacles and polyps at night to capture prey when the level of plankton in the water column is the highest. In a home aquarium most corals will also extend their feeding tentacles when the lights go out. Over time, most corals will learn to extend their polyps and eat during the day when food is present in the water. Before feeding your corals, feed your fish. Feeding fish a thawed frozen food will normally stimulate corals to begin to extend their feeding tentacles.

Do I need to switch off powerheads when feeding corals?

Before feeding corals, turn off the powerheads or circulation pump and main return pump and wait for the aquarium to become still. When feeding without a current the food can fall onto the corals so that its tentacles can grab it. Live foods like copepods can easily be captured. Leave the pumps off for fifteen minutes to an hour before turning them back on.

Depending on your circulation system, once the corals get in the habit of capturing food you may be able to leave powerheads running while feeding. Most corals should be able to capture their food. The return pump should stay off for at least fifteen minutes to an hour to allow corals to remove food from the water.

Since most reefs use a mechanical filter (filter socks, for example) the food falling over the overflow box gets trapped in it. This is obviously dependent on how large the food is and how small the pores are in the sock. Food trapped in socks will break down and produce nutrients to feed unwanted algae.

Do I need to turn off the protein skimmer when feeding corals?

Depending on your filtration system set up, it may be advantageous to turn off your protein skimmer when feeding for about two hours. A vacation timer allows you to turn off your skimmer for a specific time and automatically turns it back on, thus ensuring the skimmer does not get forgotten.

Protein skimmers do a great job of removing excess food when a reef is overfed.

How do you target feed corals?

Target feeding is a great way to control how much food goes into an aquarium. To target feed use a turkey baster, long medicine dropper, or similar feeding apparatus and gently squirt food in the direction of the intended corals. The food can be liquid phytoplankton or zooplankton; mysis shrimp mixed with aquarium water or any other coral food in a liquid form or can be mixed with water.

To target feed a soft coral mix frozen mysis shrimp with a little aquarium water. Once the shrimp has thawed, slurp the mixture up with a turkey baster. Staying several inches away from the coral, gently squirt some of the shrimp so they land on the coral. The tentacles will sense the food, capture it and within a short time you can see the food traveling to the mouth, and watch it be slowly drawn in. This entire process just takes a few minutes.

In summary

The downside to feeding corals is that if all the food is not being eaten by the corals, nutrients can build-up, thus reducing water quality, causing an algae explosion. A good protein skimmer, refugium, activated carbon, and regular water changes help keep ideal water quality with proper feeding.

If your reef already has an algae problem without feeding your corals it is best to wait until your algae is under control before attempting to feed them, or only target-feed corals very lightly.

The most important part of keeping soft corals healthy is good water quality, ideal light, and regular feedings with the right foods. Healthy, growing corals are a good indication you are feeding enough. Your best choice of coral food is live, preserved, or frozen foods.