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Saltwater Aquarium Filtration - Chemical Filtration

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Last updated on November 23rd, 2023


Saltwater Aquarium Filtration - Chemical Filtration

What is Chemical Filtration for Saltwater Aquariums

Unlike other aquarium filters, chemical filtration is typically very specific to the problem being solved. Typically this is high nitrate or phosphate, but it could also be some kind of metals or other element that is too high. While I really can't stress enough that you should find the reason for the high reading, chemical filtration will help bring everything back in check while you work to fix the problem itself.

I can't go through every form of chemical filtration media, but I will try to go through some common filter media options and problems that they can solve.

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Activated Carbon

Activated carbon is designed to remove dissolved organic compounds from the water. Activated carbon WILL NOT remove Nitrates nor Phosphates from the water.

The dissolved organic compounds that activated carbon removes is really the small particles in the water that cause the water to be yellow. Activated carbon also removes smells, toxins, and contaminants added to the tank through natural means such as corals shedding mucus or unnatural means such as spilling your coffee in the tank... Long Story...

When should you run Activated Carbon?

Honestly, most people run activated carbon constantly. This helps keep smells and toxins low while also making the water more clear. The only downside to running carbon is that it also absorbs trace and minor elements from the aquarium. So you may want to keep an eye on things with an ICP test every 3 to 6 months just to make sure nothing is going wrong.

Something to think about when using activated carbon is that there are different types of carbon you can use. Bituminous Activated Carbon is a harder form of activated carbon that has small pores for filtering small pollutants. This type of aquarium carbon rinses quickly, and is one of the cheaper options available. Lignite Activated Carbon is a softer form of aquarium carbon media that has larger pores for trapping larger particles. This type of activated carbon is slightly more expensive, but is used to catch the compounds that Bituminous carbon can't.

Finally there is ROX 0.8 activated carbon media. ROX 0.8 activated carbon is a pharmaceutical grade carbon made with both large and small pores to catch a variety of particles. It is a harder carbon that rinses easily and catches the most compounds. The trade off is that it is the most expensive activated carbon. Even being the most expensive, it's not really THAT expensive.

GFO Saltwater Aquarium Filter Media

Granular Ferric Oxide, or GFO, is a saltwater aquarium chemical filter media used specifically to reduce phosphates in reef tanks. When phosphates become too high, it can be difficult for stony corals to grow, not to mention it will lead to large algae and Cyanobacteria blooms. GFO can be used to remove phosphate, but should be monitored as phosphates that are too low can cause to poor growth and coloration in corals. Extremely low phosphate is also known to lead to dinoflagellates (dinos), which is not a pest any reef keeper wants to deal with. Unlike activated carbon, GFO should ONLY be used if it is needed, and even at that point, you should try to identify the source of the phosphates rather than just removing it chemically every time.

Using GFO saltwater aquarium filter media

GFO should only be used if you are actively measuring phosphates because your phosphates can be too low. Additionally, if you already have low phosphates, there is no reason to use GFO. When testing phosphates, I recommend using the Hanna Checker for an easy reference. When you notice nuisance algae starting to grow, this is generally a sign that your phosphate levels are elevated and you should pay closer attention to them.

Though GFO can be placed in a media bag and placed in higher flow areas of the sump, like carbon, it is more efficient to run in a media reactor. When running GFO in a media reactor, you should ensure that there is a slow, mild tumble of the media. If the media blows around too much, it will break apart and can grind into a dust that will get in the water column. Additionally, too slow of flow, and no media tumbling can lead to the filter media clogging and becoming a nitrate factory, as well as not removing phosphates.

Before using GFO it is very important to rinse the media to remove the red dust before it is added to your tank. If you are using mesh bags, you can simply run this under tap water until it is clear, then quick rinse it with RO water before adding it to your sump. If you are using a media reactor, you can just run the reactor in your sink until it runs clear, then rinse the tap water off with RO water.

How often should I replace GFO filter media?

GFO can work for weeks to months without being replaced, however this will be different for every aquarium. This is due to the different phosphate levels, as well as how much water is flowing through it. To know when to replace the GFO in your aquarium, simply test your phosphate levels and if phosphates are not decreasing, its time to replace.

Carbon Dosing with Bio Pearls / Bio Pellets

Bio Pearls are a chemical filter media used to reduce nitrates in the saltwater aquarium. Bio pearls work much like vodka or carbon dosing. The bacteria that consumes nitrates, and is removed by the protein skimmer, use this carbon to reproduce quicker. These bio pearls provide a source of carbon for the bacteria to reproduce and consume more nitrates. Meaning this chemical aquarium filter is more of a crossover between biological and chemical filtration.

For more information about Carbon Dosing, check out the article Carbon Dosing for Reef Tanks.

When using bio pearls, they should be placed in a media reactor and forced to tumble as much as possible. Bio pearls don't work by blocking particles but rather by slowly dissolving as nitrate consuming bacteria require them. By forcing them to tumble, there will be more water in contact with the surface of the pearls as well as less debris buildup, leading to lower nitrate levels.

Seachem Purigen

Purigen advertises benefits similar to that of activated carbon, with the added benefit of ammonia and nitrogen reduction. Though I have not personally used this chemical aquarium filter media, I would not replace activated carbon just yet. A cycled aquarium should not have any ammonia or nitrites present. Therefore, this chemical filtration will provide benefits similar to Bio Pearls for reducing nitrates. Therefore, I would recommend looking in to Seachem Purigen only if you are looking to reduce nitrates, and would like the added benefits not offered by bio pearls. Though I have not used this, there are positive reviews making me believe it is worth mentioning.

Boyd-Enterprises Chemi-Pure

Boyd-Enterprises Chemi-Pure is essentially a blend of activated carbon with other chemical saltwater aquarium filter media. They advertise additional ionic benefits in addition to PH stabilization. Again, this is a chemical filtration I do not use because the main features are the same as activated carbon, however, some of the added benefits, like the ability to remove copper and other toxins may be worth considering. I would recommend this product mainly for removal of organic compounds if you have already tried activated carbon without success. This would be the next level of filtration if carbon didn't solve your problem.

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About the Author

Reef Stable Founder John Krenzer

John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.

Today, John maintains an over 300 gallon reef tank system, consisting of a 120g reef and a 210g reef. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.

John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.

If you would like to request an article, tank tour article, or to collaborate, let me know via the Contact Me Page!

About Reef Stable

Reef Stable was initially founded in 2019 as a reef tank parameter log to fill a need. Reef Stable quickly grew, becoming a location to solve all of your reef tank problems as well as a place to learn.

Reef Stable now provides a Reef Blog, Reef Aquarium Guides, Coral Care Guides, Identification and Solutions for Pests and Algae, and Reef Dosing Calculators, in addition to the original Reef Parameter Log.

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