5 Minute Saltwater Aquarium Guide Episode #23 - Activated Carbon

It is time to talk about carbon. Ryan gives us the full carbon rundown including exactly how it works, why you would use it and how to employ carbon effectively on your very own reef aquarium.


Yellow Water


Why Use Carbon?

Your protein skimmer and water changes will keep nutrient levels down and export waste but they will not stop the water from yellowing. Yellow water is just the end result of all the organics, food and fish waste breaking down. The yellow water is not just visually undesirable but also blocks light from penetrating through the water column, reducing energy to the corals. Essentially a sign of poor water quality and generally comes with a foul odor as well.


The blue lighting on our reef tanks makes it difficult to see exactly how yellow the water gets. You can see it best when the lights are off and looking through the tank, from end to end. It will become quite obvious when the area on the other side of your tank looks yellow.


Bucket Test


When doing a water change, it is also quite obvious. Simply compare your freshly mixed saltwater with your old tank water. If they don’t look the same, it is time to polish your water with activated carbon. Running carbon as a water polisher will turn the water back to its original pristine blue color.


What Is Activated Carbon?

Activated Carbon is the most widely used water filtration media on the planet and used in a myriad of different industries, not just for aquariums or aquatic life support. You have probably seen carbon in your drinking water filters and in your RO/DI system.


ROX 0.8 Carbon Granules


Carbon is made of a vast microscopic pore network designed to adsorb pollutants. The media has so much surface area it is somewhat difficult to grasp, in fact, a single teaspoon of carbon has as much surface area as an entire football field. That’s partially what makes it so good at removing these common water pollutants.


How To Use Activated Carbon

In an aquarium, most reefers simply drop a filter bag of carbon in a high flow area of the sump or tank. You can also run a fluidized media reactor that pumps water through the media increasing contact with the media for more efficient adsorption.


BRS Deluxe Carbon and GFO Reactor


Our BRS reactors are uber-popular because they are affordable and the small canister/cartridge combo is easy to clean and maintain.


In our two tanks here, we are going to do things a little different. For the 40-gallon breeder, we are using an Eheim Liberty Power Filter. Power filters are generally inexpensive and hang on the side or back of your tank for a simple and clean installation.


Eheim Liberty Filter Carbon Cartridge


Operation is simple, the Eheim Liberty just needs to be primed with water after plugging it in and you are ready to go. Inside the filter chamber there are pleated filters cartridges with activated carbon inside them. The little carbon filled cartridges not only polish the water but will also remove floating particulates. The filter cartridges are disposable and when exhausted, simply swap out with a new one.


A much more economical approach is to use a mesh bag with drawstring to hold loose carbon instead. You can then place that filter media bag anywhere with high water flow so inside a hang-on power filter, like the Eheim Liberty, in your sump or in the back filter chambers of your AIO tank.


BRS ROX 0.8 Carbon


The best carbon we sell is the Bulk Reef Supply Rox 0.8 that is designed for the pharmaceutical industry and has a range of benefits over traditional granular or pellet carbon.


  • Pharmaceutical grade purity
  • Vast range of pore sizes
  • Low Dust

A 1/4 cup of carbon at one time is adequate for a 40 gallon tank. The small 0.75 lb container will last you for the better part of the year if not all year long.


Carbon bag in Red Sea E170 Media Basket


The Red Sea E170 has a convenient media tray in the back filtration compartments to hold media. The baffle system ensures water flows through the media and overall is an effective and inexpensive way to polish your water using carbon.


Regardless of your method or type of carbon used, be sure that it is rinsed thoroughly with cold water prior to use. This will wash away any residual dust or fine particles that could escape the media bag into your tank.


Rinsing carbon under tap water


Using RO/DI water to rinse the carbon is ideal but certainly not practical, thousands of hobbyists before us and thousands ahead of us will continue rinsing in tap water without any problems.


Change carbon monthly or every 2 to 4 weeks but more precisely when you see the water turning yellow in the tank. Try out that bucket test when you do your water changes and you will not only get the hang of it but acting on data and be doing it better than most.


Sump with refugium


What’s Next

In addition to yellow water, there is a slew of additional pollutants in your tank water, most notably phosphate and nitrate. If you have implemented a reliable and stable solution for phosphate and nitrate control in the first year of reefing, you can count yourself in the top ten percent of first-year reefers as avoiding a major challenge which often results in undesirable algae growth.



One of the most effective and coolest ways to export extra waste and nutrients from your reef tank is with a refugium which is conveniently our next topic in the 5 Minute Saltwater Aquarium Guide.


5 Minute Saltwater Aquarium Guide Episode #24


Looking for a different topic or have questions? You can binge the entire 5 Minute Saltwater Aquarium Guide playlist right here on our website. We also invite you to join the #askBRStv Facebook Group which is a free resource for you to ask questions, get advice, interact with other hobbyists and get your daily reef aquarium fix.


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