How to Cure Rock for Your Reef

In the early days of reef keeping live rock was harvested from unprotected reefs, shipped by air and then trucked to your home. It was exciting because you never knew what marine life would pop out of the rock. We all hoped for corals and other interesting creatures but we mostly got a lot of dead marine life that decomposed and fouled the water. You couldn’t just drop the rock into your tank and expect it to be reef-ready, so collectively hobbyists developed the concept and method on how to "cure" live rock.

Curing is a way of preventing fresh live rock from ruining your main aquarium. There are countless stories of fresh live rock causing ammonia spikes, cloudy water and hydrogen sulfide gas build-up in aquariums. Think of curing like a quarantine process for live rock. It allows the “bad stuff” to happen outside of your aquarium. Here are some of our tips on how to cure live rock for your reef.

Why Do I Need to Cure Live Rock?

Live rock is usually aquacultured in the ocean instead of being chipped off a natural reef. The idea is to seed the rock with reef-friendly marine life like coralline algae and especially beneficial microbes that eliminate nitrate and other wastes. Anytime live rock is harvested, packed in a box and shipped there will be some die-off of the attached marine life. When the rock is placed in an aquarium the organic matter starts to decompose. This often causes a spike in ammonia, phosphate and release of organics into the water. Curing isolates this process from your main aquarium by allowing it to happen in a smaller container, like a 55-gallon trash can.

What Equipment Do I Need to Cure Live Rock?

The main consideration is the amount of live rock you plan to cure. If you’ve only got a few pieces of rock for starting a nano tank you can do it in a 5-gallon bucket of saltwater. For larger amounts of rock many aquarists use 55-gallon trash cans. You want to have enough room to fully submerge the rock. Use an air pump and air stone to circulate the water and loosen debris and dead organisms. Chances are there’s going to be a lot of oxygen-consuming decomposition. Aeration drives off excess carbon dioxide and hydrogen sulfide and keeps the water oxygenated. You can also use a powerhead to move water and flush the rock. If you’re curing the rock in a cold basement, add a submersible heater. Set the temperature to about 78F. Curing requires a lot of water changes to flush away ammonia, organics and other debris. You may want to have a separate salt-mixing container so you’ll always be ready to make a water change.

Preparing Live Rock for Curing

When your live rock arrives immediately open the box and examine the rock for dead algae, crabs, sponges and other marine life. Poke around for crustaceans caught in the cracks and crevices. Remove anything that looks dead. Brush off loose material.  Place the rock in a container of saltwater along with an air stone or powerhead.

What About Dry Rock?

Dry rock is natural live rock but has been completely dried in the sun. It contains no living organisms. Even though it is completely dry, it can leach nutrients and organics as the dead marine life decays in the water. It should be cured like live rock. Check the water for ammonia and odors during the cure. There are exceptions. AquaMaxx and CaribSea South Sea base rock are all-natural dried reef rock mined in Florida. Caribsea’s Life Rock is aragonite rock with a purple coating that looks like coralline algae. Over time living coralline will cover the rock as the tank matures. These products need no curing since they don’t contain living or dead organisms. All that’s needed is a quick rinse and they’re ready to use.

The Curing Process

If the rock contains a lot of decaying organisms, it can take several weeks or even months for it to cure. Test the water after a few days for ammonia. It will give you an idea if there’s a lot of decay. If the water or the rock has a rotten egg (sulfur) odor, it’s a sign of decay too. Water changes flush away organics and ammonia, and prevent the rock from sitting in dirty water. Weekly water changes are recommended.

Knowing When the Curing Process is Finished

It’s not possible to predict when your rock will be ready to add to your aquarium. It all depends on how much decomposing organic matter is locked up in the porous rock surface. The best advice is to make frequent water changes and test for ammonia. When the ammonia remains at zero, you know there’s no more decay. The rock should also be free of sulfur odors.  Now you can safely add the rock to your tank.

What to do After Adding Live Rock to Your Aquarium

Even after going through the full curing process, be sure to test your aquarium’s water for ammonia for a few days after adding the rock.  That way there’ll be no surprises if the rock still has some organic matter in the cracks. Watch the protein skimmer too. It’s normal to see an increase in foam for a week or so. But excess foaming is a sign there’s still some curing going on. Once you’re sure the rock isn’t releasing ammonia or organics, begin building up the reef with corals and other marine life. It’s a good idea to add a bacteria starter too. It can help kick off the biological filter and help speed the maturation of your tank.