8 Tips for Curing Your Dry Rock

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1.  Clean & rinse the rock manually before you start:

Most of the dry rocks on the market like the Fiji, Pukani, or Tonga rock are rock that came from the sea but have been allowed to dry out.  This means that they are often covered in various types of organic matter.  There might be dried out sponges or other critters on the outside of the rock.  Once in a blue moon you might find a larger creature as well.  These are the things that break down in the tank to produce ammonia, nitrates and phosphates in the water.  The more you can do to manually remove them before you start the curing process, the less time the process will take.  There is a notable exception to this though.  The Reef Saver rock is a natural calcium carbonate rock that doesn’t come from the ocean.  It comes in pre-washed, so a simple rinse to get rid of the dust should be sufficient.

2.  Use the rock itself to cycle the tank without livestock:

In order for a tank to properly “cycle” you are relying on colonies of beneficial bacteria to grow that process toxic ammonia to less toxic by-products.  These bacteria process ammonia (a large component of fish waste) to nitrite and then a different type of bacteria process the nitrite to nitrate.  The bacteria themselves aren’t going to grow if they don’t have any food though (ammonia).  Some people accomplish this in a new tank by adding fish. The fish produces waste (and as a result ammonia), the waste acts as a food source for the bacteria. The downside is that the fish’s waste accumulates until there is sufficient enough bacteria to process the waste.  The fish may die before sufficient bacteria has had time to form (this process can take over a month).

You can use organic matter on the rock to your advantage.  Rather than adding a fish or a different type of critter to the tank, the organic matter on the rock breaks down and creates ammonia.  This creates a sufficient food source for the bacteria to grow.  No need to add a fish.  If you have heard of people adding things like dead shrimp to the tank to start this process, using the rock is basically the same thing.  A notable exception to this is the Reef Saver.  Not having the organic matter means that there isn’t anything to break down and become ammonia.

3. Keep it warm:

Most bacteria tend to grow faster at warmer temperatures.  Make sure to keep a heater in with your rock and at least keep the water temperature close to aquarium temps (78 degrees or so).  Some folks even raise their water temperature into the low 80’s to try and speed the process up a bit more.  If nothing else, it is a good idea to cure the rock in parameters that will be similar to that of the aquarium.

4. Test it (but not too often):

The way to know if your rock is finished, is to monitor the parameters of the tank.  The most important parameter is ammonia.  This is the most toxic to your fish and one of the first things produced by the decay of the organic matter on the rock.  You do not want to add fish to water that contains ammonia and you also want to wait to add fish until you are sure there is a sufficient population of bacteria to process the fish waste.

To do this, test your water with an ammonia test kit.  As the organic matter on the rock breaks down you will see the ammonia levels continue to rise.  After a few weeks you will see the ammonia level start to drop.  Bacteria grow at exponential rates, so once it begins to decrease, the rate at which it starts to decrease rises very quickly.  For example, the ammonia levels will often rise slowly from say 0ppm to 5ppm over the course of weeks.  Then in one day it might go from 5ppm to 4.5ppm, the next day from 4.5ppm to 3.5ppm, and the third day from 3.5ppm to 0.  It isn’t your test kit lying to you. :-)

The ammonia is being converted to nitrite, so you should see a subsequent increase in the nitrite levels during this time.  As the rock continues to mature, you will see a similar process with the nitrite levels.  It is generally considered safe to use the rock once the water has 0 ammonia and 0 nitrite levels.

Testing is the way to know when your rock is done, but don’t test yourself into insanity!  I would suggest testing it weekly.  Testing it daily tends to just be disheartening, as you are so excited to start seeing ammonia levels decrease.  When you are testing every single day and it only goes up it tends to make you a little crazy!

5. Use a bag of carbon:

The water you are curing your rock in can get pretty nasty.  As all the organic matter breaks down the water will turn yellow and it is not that unusual for it to begin to smell pretty bad.  Letting it smell is usually a pretty good way to convince your significant other that you shouldn’t have an aquarium. :)  Fortunately the solution to this is super easy.  Just use some carbon.  It doesn’t need to be a fancy process, simply putting some carbon like our lignite carbon into a mesh filter sock/media bag.  You will be amazed with how quickly (hours) the smell will go away as well as the color in the water.

6. Leave the lights off:

Bacteria don’t need the light to grow and start processing the ammonia (at least not the type of bacteria you want!).  Do you know what does love light and high ammonia water?  Algae!  At this point there isn’t any coral or livestock in the tank to need light so just leave it off.  Otherwise you are likely going to have a sea of green before too long!

7. Do a 100% water change when you are done:

Your aquarium just spent a lot of time breaking down all the organics on the rock into more basic components like ammonia, nitrite, nitrate, and phosphate. If those things sound like what you read on the back of a bag of fertilizer, it is because it is.  Ammonia/Nitrate and phosphate are major nutrients for growth of plants and algae.  The levels of these nutrients have to be kept to a minimum in a reef tank because they can cause corals to brown, slow growth, and cause nuisance algae to grow like crazy.

You don’t want to start your new tank out on the wrong note, so you want to get rid of all of the nutrient laden water. If you are doing this whole process in your aquarium, you will want to do a 100% water change.  Drain all of the water out of the tank and replace it with new sea water.  It will be just fine to be out of water for a short period of time while you do this.  Doing two 50% water changes also is not the same thing.  A single larger water change will remove more of the nutrients.  For example, a tank with 10ppm nitrate given a 100% water change will be 0ppm.  The same tank with a 50% water change would be 5ppm and giving it a second 50% water change would reduce the 5ppm to 2.5ppm.

If it isn’t feasible for you to do a 100% water change in your aquarium, it would be best to cure the rock in a separate container (Rubbermaid container, trash can, etc).  This way you can have an aquarium full of new tank water and moving the rock from the old water to the new water is basically the same thing as a 100% water change.

8. Be patient:

This one largely speaks for itself, but be patient with the process.  It takes a certain amount of time for all of the bacteria to grow and process the ammonia and nitrite.  Weeks to months is the norm and every tank will be different.  Nothing needs to be done to add the bacteria.  They are ever present and will grow on their own, though some people choose to add a liquid bacteria product to try and get the process started faster.

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