Adding corals to your reef can sometimes be a tough decision of weighing out pros and cons. Do you have the right lighting, flow, water parameters, and nutrient levels? Will they be compatible with your fish and inverts or are they likely to end up on the menu? Will they spread and overrun your tank? Are they SPS, LPS or softies, or something even trickier like a non-photosynthetic coral? And which actual species or variety are they? All these thoughts of buying a healthy coral frag go through the minds of new reefkeepers (and even veterans) and just like buying fish, you need to consider the coral’s health, when you should buy it, and when you should leave it where it is. So here are some signs to look out for in choosing a healthy coral.

Soft Corals

Soft corals should look lively with polyps fully extended, so if they look small and tightly retracted, it should be avoided. Although there are some coral, like leather coral, which have a habit of retracting their polyps and shedding mucous, you still should only buy them if their polyps are extended.

Illustration of a healthy zoanthid coral vs unhealthy zoanthid with pests

Zoa and Paly polyps should look like they are reaching and fully extended; good signs of a healthy coral colony. Don’t buy a Zoa plug where you can’t see the polyps extended. It may have parasitic hitchhikers or have spent too long in the wrong conditions, weakening it.

Other softies, like mushroom corals, should look expanded and wavy, too. They are usually overlapping each other, covering a whole rock or frag plug. However, if they are shrunken and tight, it typically means they’re either not happy or may not ready to buy yet.

Green star polyps, Clove polyps, and Xenia should all be fully extended. If the base of their mats start to come apart, floating off, or the majority of polyps are either retracted or very small, they may be dying.

LPS Corals

One of the best signs when buying a healthy LPS coral frag is that the polyp (or head) looks fully inflated, and bouncy with a gentle motion in the water flow. Avoid frags where some of the skeleton is showing or the coral tissue looks to be melting or rotting away. Some LPS have powerful stinging tentacles and can literally sting and devour their neighbor’s flesh. If a coral is missing tissue on one side it may have lost a fight with its neighbor, and may not have much strength to acclimate to a new tank.

Illustration of a healthy scolymia coral vs unhealthy scolymia with receding flesh
Example: Healthy LPS vs LPS with skeletal structure showing

Branching LPS should be fully extended with each head intact. They can be prone to brown jelly disease or flatworms, which will spread to others of their own kind. If the frag is to be cut from a colony, observe that the other heads are open and looking healthy.

Don’t buy any LPS frag where the polyp looks like it is shrunk up as you won’t be able to tell if it is healthy or if there’s something wrong with it. Avoid any LPS where the flesh looks like thin skin draped over the spiny skeleton underneath. You shouldn’t be able to see the skeleton at all, under the polyp head.

SPS Corals

SPS are the least forgiving corals when you buy them. They may be frags from another reefer’s tank, LFS, maricultured (farmed in the sea), or taken from wild colonies. Wild SPS are often the most difficult as they will be stressed from collection and travel, followed by acclimation to completely different lighting and nutrient levels than they are used to.

Illustration of a healthy SPS coral frag vs unhealthy zoanthid suffering from tissue necrosis
Example: Healthy SPS vs SPS with tissue necrosis

Whether it’s on a frag plug, cultured base, or a loose colony, signs of a healthy frag is an entire skeleton covered in coral tissue, unbroken, and with tiny polyps visible all over. Avoid any SPS frag which is white at the base as that tissue necrosis may quickly rise up the frag and kill the coral in days. SPS can “strip” meaning some or all of the tissue dies off exposing the white, dead skeleton. An experienced SPS grower may be able to cut off the dead sections and save some of the living frags, but sometimes nothing can save it and it will be completely stripped and dead the next day.

SPS can bleach, where the tissue turns very pale to white all over. This can be shock from a few things such as too much light, not enough flow and nutrients, or from high temperatures. Although some SPS are meant to be pastel-colored, if it’s white, leave it where it is - it’s more than likely it is not a healthy coral.

SPS can also turn brown from too many nutrients being present, which many experienced reefers may look at as coral with color potential. So, as long as it has polyp extension and all its tissue, don’t be put off because with proper acclimation to the right conditions, it may turn into something beautiful.

SPS do make a feeding response too, which is a good sign of health. Their tiny polyps should become slightly larger and fluffy, or even fur-like when triggered. If it shows better polyp extension when food is added to the water it would be a good pick as a healthy coral frag.

Before you Place the Frag in Your Tank, DIP!!

All new frags or colonies should be dipped to help prevent the spread of pests and diseases to your reef tank. If you can, quarantine the frag in a separate system. If you can’t quarantine, place it in a temporary spot where it can be observed like on the sand or a frag rack, this way you see any pests or their eggs and can then still remove the frag to dip again. It may take multiple treatments over time to rid it of any nasties, before the frag can be mounted permanently.

What to do if your coral doesn’t come out in your tank:

If the coral frag looked healthy and its polyps were fully extended when you were buying it, but they won’t come out in your tank, you may have a problem. Check temperature, salinity, KH, Calcium, Magnesium, nitrate, and phosphate. Next, think about where you placed it. Is it receiving more or less light than it did in the store? More or less flow? Are your other corals looking happy and extended like normal? The new frag may just need to be moved into a new position, until it finds it's sweet spot.

Another thing to look out for are your fish. Many LPS corals are susceptible to being nibbled by Angelfish so its best not to mix them. Aiptasia eating fish or inverts are capable of eating a coral polyp as they would an Aiptasia anemone.

Anemones with clowns hosting often have an invisible radius where no fish or coral are allowed. Clownfish may try to pick up a frag that is too close to their nem and move it away. So, place new corals away from other corals and anemones so they don’t get stung. Anemones are mobile too, so be cautious.

Final Thoughts

illustration of coral frag inspection

Inspecting before buying, then dipping when you get home and observing after you place it in its permanent location will ensure a healthy coral frag. Dipping a coral even if you think it is free of pests increases survival rates of the frag and lessens the chance of spreading disease to the other corals in your tank. So, be sure to inspect, dip and observe!