Bleach Curing Dry Rock for a Saltwater Reef Tank - BRStv Reef FAQs

April 29th, 2019
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There are three main methods for curing live rock for a saltwater reef tank: natural, bleach and acid. Our focus today is using bleach for curing dry rock and we answer three direct questions. 


  • 1. What is a bleach cure?
  • 2. When is it appropriate to bleach cure rock?
  • 3. How to do it?


Bleaching dry rock or a “bleach cure” involves soaking the rock in a diluted solution of water and bleach. The bleach will oxidize and rapidly break down organic material on the surface of the rock. In many cases, you can get a complete bleach cure done in about 7 days making a longer “natural cure” unnecessary. 


The primary advantage of a bleach cure is the speed but it is also going to kill basically anything living on the rock’s surface including algae spores and undesirable bacteria. This is very appealing to many reefers who prefer to start from ground zero because it reduces the risk of introducing harmful hitchhikers and annoying nuisance algae


Phosphate Levels of Cured Rock


We did a BRStv Investigates video on curing rock where we found soaking for a week in a bleach solution cleaned the rock so well that there was no residual nutrient spike during the following natural cure. This means a residual natural curing procedure is not necessary after performing a bleach cure.


Brightwell Aquatics EraseCL and LaMotte Chlorine Test Strips


Is bleach safe for a reef tank? Yes, when used in this manor. 


In fact, if you let the rock completely dry out, the bleach would simply gas off and be reef safe again. We chose to use a dechlorinator and some test strips just to be sure.


While not as safe as a natural cure in which you simply let the rock soak for a long time in saltwater, a bleach cure is perfectly safe for anyone willing to put in the effort required to do it properly.


To Cure or Not to Cure...Using Bleach

Deciding whether a bleach cure is appropriate depends on the type of rock you have. Wet live rock, dry rock from the ocean, mined dry rock, and man-made dry rock will each require a different approach to curing with bleach.


Different types of Live Rock and Dry Rock


Wet Live Rock - Don’t Do it

In the case of wet live rock from the ocean that is full of life, a bleach cure is not exactly a logical solution because it will kill all of the living organisms you paid a premium for.


Dry Rock From The Ocean - Do It

Rock from the ocean, or a previous tank, that was left to dry is often covered in dried or dead organics and is a prime candidate for curing with bleach. You can dramatically reduce the organic content of the rock and kill everything including spores, dormant bacteria and various other undesirables. 


Dry Mined Rock - Don’t Do It

If you are using a dry mined rock like Marco Rocks Reef Saver, it is super clean out of the box and an aggressive bleach cure is unnecessary for that reason. If you are extremely diligent about preventing pests you could do a short bleach cure just to insure no spores or anything else is on the rock.


Man-Made Dry Rock - Don’t Do It

Similar to mined rock, man-made dry rock such as the Real Reef brand do not warrant a cure in bleach. In fact, a bleach solution could very well have an effect on the purple color some of these rocks use. 


Bleach chemical warning


WARNING - Bleach is a chemical with inherent safety risks. Although bleach is a household chemical, curing aquarium rock is not the intended use so there are other risks involved not listed on the bottle. Do not perform a bleach cure if you are not willing to take the necessary safety precautions and educate yourself accordingly.

Do not do this indoors, bleach can create very toxic gasses. Always perform a bleach cure outdoors in the open air with a proper ventilator. Always use appropriate safety gear including arm length gloves, goggles, and protective clothing. 


Wearing protective gear during a bleach cure of live rock


How to Bleach Cure Dry Rock

This is not an exact science, much of what the hobby knows is based on sharing personal experiences so we advise that you research and discuss the process of bleach curing with other hobbyists who have experience. The exact ratio of bleach to water or bleach to rock is not universally agreed upon. 


Step #1 - Find a container large enough to hold all of your rock. Bring it outside and fill it with water, in most cases it will likely be something like a Brute trash can. Most reefers like to use purified RO/DI water but in this case, tap water is suitable as well. 


Step #2 - Add the bleach. Be sure to use bleach that is free of additives, scents and soap. The unofficial but general recommendation is one gallon of bleach for every 10 gallons of water. This 1:10 ratio is what we used during our #brstv investigates video and is more of a reefing community suggestion than a precise figure. 


Always add the bleach to the water and not water to bleach. This will reduce the chances of splashing concentrated solution around and undesirable reactions. Under no circumstances, add any additional chemicals. Mixing bleach with other chemicals can produce deadly gases. 


Step #3 - Add the rock carefully to your bleach solution and then wait one week (7 days). By the end of the week there is a good chance a vast majority of the organics will have broken down and the rock is ready for use. If not, you can always add more bleach and wait another week before using it. 


Step #4 - Once the rock is clean and done soaking, remove it from the bin and give it a quick rinse. Technically speaking you can just let it completely dry out and that would gas off all the excess chlorine (deadly to fish and inverts) but don’t rely on that alone. Fill the container back up with clean, purified RO/DI water and dose a healthy amount of dechlorinator to eliminate any residual chlorine. Brightwell Aquatics Erase Cl or Hikari’s ChlorAm-X are both excellent options. Let it soak for an additional 24 hours and test the water using chlorine test strips to be confident the chlorine has been removed. 


Helpful Tip: Leftover chlorine test strips can be used to know when to change your carbon block filters inside your RO/DI system. Watch our BRStv video on the subject to learn more!


Finally, give the rock a final manual rinse with RO/DI water and it is now free of organics and harmful pests and ready for cycling. 



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Watch Video: BRStv Investigates: What is the best way to cure dry live rock?

Watch Video:Natural curing live rock for saltwater fish tanks? - BRStv Reef FAQs

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