Saltwater Aquarium Blog

Large Polyp Stony Corals

Large Polyp Stony Corals

Coral husbandry is best studied on an individual species basis—because there are exceptions to every rule and generalizations (like the one I’m about to make) often oversimplify the information.

Putting my desire for precision and my inner-scientist aside, however, the value of generalizations is that they provide a jumping-off point—a lens through which to observe, consider and start to pursue additional information.  One such generalization is the categorization of coral species into a group commonly called Large Polyp Stony (LPS) corals.  To the newcomer to the hobby, these corals look like a sort of hybrid between the soft corals and small polyp stony (SPS) corals. 

Hammer Coral

The species generally categorized as LPS have a stony backbone and large, fleshy polyps.  Some marquis examples of this are the Hammer Corals, Torch Corals and Frogspawn corals of the genus Euphyllia, or the Bubble Corals of the Plerogyra and Physogyra genuses.  These corals are often from deeper, slower moving, sometimes turbid water.  As such, they typically require low-to-moderate lighting and flow.  They tend to be aggressive feeders, so direct feeding of meaty foods is often recommended.  They should never be removed from the aquarium while the polyps are inflated, or serious damage can occur. Several members have considerably lengthy sweeper (stinging) tentacles, so care should be given to placement.

Since large polyp stony corals have a calcified external skeleton, it is important to monitor and control for alkalinity and dissolved calcium level. Insufficient levels of calcium will result in erosion of the skeleton and eventually death of the organism.  Sufficient levels can sometimes be achieved with the regular use (and exchange) of saltwater made from a high quality salt mix, although supplementation may be necessary to maintain optimal calcium/alkalinity levels in between water changes.  Arguably, the more involved managing of water chemistry is of the things that make large polyp stony corals (LPS) more difficult to keep than their soft-bodied cousins.

Saltwater Aquarium Blog Tip: Purchase a good calcium test kit and try to keep the dissolved calcium level above 400ppm through water changes and supplementation.  To determine if you’ll need supplementation, mix a bucket of saltwater, let it sit a day and then test—that is your baseline. Is your calcium already over 400 ppm? If not, you need to supplement. Also consider that the corals will extract calcium from the water over time, so you will need to regularly monitor and dose to keep up with the calcium demand in your tank. The more LPS you have in your tank, the higher the demand for calcium will be. 

Advanced Aquarist Note: Eventually, if you continue to add large polyp stony (LPS) or small polyp stony (SPS) corals to your tank, you may want to consider adding a calcium reactor/pump.  These are not for the casual hobbyist, as the price tag is often in the hundreds of dollars, but to maintain productively high levels of dissolved calcium, they are an important piece of equipment and a time saver.  A calcium reactor creates a basic chemical reaction to release calcium ions from a solid substrate into your tank.  To accomplish this, carbon dioxide is injected into the reactor chamber, lowering the pH.  The pH drop causes the substrate to dissolve, releasing dissolved calcium ions that can be absorbed by your corals.