Maintaining exceptional water quality is one of the keys to a thriving reef aquarium. While biological filtration and mechanical filtration often take centre stage, chemical filtration media plays an equally important role in removing dissolved impurities, controlling nutrients, and creating the crystal-clear water that allows corals to flourish.
From activated carbon and phosphate removers to specialised resins and mixed media, chemical filtration can significantly improve water quality when used correctly. Understanding what each type of media does—and when to use it—will help you create a healthier, more stable marine aquarium.
In this guide, we’ll explain the different types of chemical filtration media, how they work, and how to choose the right products for your reef tank.
What Is Chemical Filtration?
Chemical filtration removes dissolved substances from aquarium water through chemical reactions or adsorption.
Unlike mechanical filtration, which removes visible debris, or biological filtration, which processes waste biologically, chemical filtration targets invisible contaminants such as:
- Dissolved organic compounds
- Yellowing compounds
- Phosphate
- Silicate
- Heavy metals
- Medication residues
- Toxins released by corals
- Unwanted chemicals
These contaminants can affect coral health, encourage nuisance algae, and reduce water clarity if left unchecked.
Why Is Chemical Filtration Important?
A good chemical filtration system provides several benefits.
These include:
- Crystal-clear water
- Improved light penetration
- Reduced phosphate
- Lower dissolved organics
- Healthier corals
- Better water clarity
- Reduced odours
- Improved overall stability
Chemical media complements your existing filtration rather than replacing it.
Activated Carbon
Activated carbon is one of the most widely used forms of chemical filtration.
Its extremely porous structure adsorbs dissolved organic compounds from the water.
What Does Activated Carbon Remove?
Activated carbon helps remove:
- Yellowing compounds
- Organic pollutants
- Coral toxins
- Medication residues
- Odours
- Water discolouration
It leaves the water looking noticeably clearer while allowing aquarium lighting to penetrate more effectively.
Benefits
- Improves water clarity
- Removes toxins produced by soft corals
- Reduces dissolved organics
- Safe for continuous use
- Easy to replace
Activated carbon is suitable for almost every reef aquarium.
Phosphate Removal Media (GFO)
Granular Ferric Oxide (GFO) is one of the most effective methods of controlling phosphate.
Phosphate fuels nuisance algae growth and can reduce coral calcification if allowed to accumulate.
What Does GFO Remove?
Primarily:
- Phosphate (PO₄)
Some products also remove:
- Silicate
Benefits
- Reduces nuisance algae
- Improves coral colour
- Supports SPS growth
- Lowers phosphate gradually
GFO is commonly used in media reactors for maximum efficiency.
Aluminium-Based Phosphate Removers
Some phosphate removers use aluminium oxide instead of iron.
Advantages include:
- Fast phosphate reduction
- Lower dust production
- Effective silicate removal
However, excessive use should be avoided, particularly in aquariums containing sensitive soft corals.
Mixed Chemical Media
Several manufacturers produce combination media that contain multiple filtration materials in one product.
These often combine:
- Activated carbon
- Phosphate remover
- Organic absorbers
These products provide convenient all-in-one chemical filtration for many reef aquariums.
Purigen®
Purigen is a synthetic filtration resin designed to remove dissolved organic waste before it breaks down into ammonia, nitrate and phosphate.
Unlike activated carbon, Purigen targets nitrogen-containing organic compounds rather than simply polishing the water.
Benefits
- Crystal-clear water
- Reduces dissolved organics
- Helps control nitrate
- Reusable after regeneration
- Long lifespan
Many aquarists use Purigen alongside activated carbon.
Ion Exchange Resins
Ion exchange media selectively remove specific dissolved substances.
These specialised products can target:
- Nitrate
- Heavy metals
- Ammonia
- Copper
- Silicate
They’re often used when addressing specific water quality issues rather than for routine filtration.
Heavy Metal Removal Media
Copper and heavy metals are highly toxic to marine invertebrates.
Specialist chemical media can remove:
- Copper
- Zinc
- Lead
- Other dissolved metals
These are particularly useful after medication or when using second-hand aquarium equipment.
Silicate Removal Media
Silicate encourages diatom blooms, particularly in newer aquariums.
Silicate-removing media can help eliminate:
- Brown diatoms
- Silicate from tap water
- Residual silicate entering through RO systems
Although many phosphate removers also absorb silicate, dedicated products are available where needed.
Carbon vs GFO
These two media are often confused, but they perform very different functions.
Activated Carbon
Removes:
- Dissolved organics
- Water discolouration
- Coral toxins
- Medication residues
GFO
Removes:
- Phosphate
- Some silicate
Many reef keepers run both simultaneously for complete chemical filtration.
Using Chemical Media in a Media Reactor
Media reactors force aquarium water evenly through filtration media.
Advantages include:
- Maximum contact time
- Better media efficiency
- Reduced channelling
- Improved phosphate removal
- Easy maintenance
Reactors are particularly effective for:
- GFO
- Activated carbon
- Mixed media
Fluidised reactors are especially popular in reef aquariums.
Using Media Bags
Many hobbyists simply place chemical media inside mesh media bags.
Benefits include:
- Low cost
- Easy installation
- Suitable for smaller aquariums
However, water flow through media bags is generally less efficient than using a reactor.
How Often Should Chemical Media Be Replaced?
Replacement schedules depend on the product.
Typical guidelines are:
Activated Carbon
Every 3–6 weeks
GFO
Replace when phosphate begins to rise.
This may vary between two weeks and several months depending on nutrient levels.
Purigen
Regenerate when it turns dark brown.
Mixed Media
Follow the manufacturer’s recommendations.
Can You Use Too Much Chemical Media?
Yes.
Overusing chemical filtration can sometimes create problems.
Examples include:
Excessive Carbon
Very large quantities may remove beneficial dissolved organics too aggressively.
Excessive GFO
Rapid phosphate reduction may stress corals, particularly SPS species.
Phosphate should always be reduced gradually.
Over-Polishing the Water
Ultra-clean water can sometimes reduce nutrient availability for corals.
Successful reef keeping is about balance rather than eliminating every measurable nutrient.
Choosing the Right Chemical Media
Your choice depends on the specific needs of your aquarium.
New Reef Aquarium
Consider:
- Activated carbon
- Phosphate remover (if required)
Mature Mixed Reef
Often benefits from:
- Carbon
- GFO
- Occasional Purigen
SPS-Dominated Reef
Typically requires:
- Activated carbon
- GFO
- Regular phosphate monitoring
Soft Coral Aquarium
Activated carbon is particularly valuable because many soft corals release chemical compounds that may affect neighbouring corals.
Signs Your Chemical Filtration Is Working
A healthy aquarium often displays:
- Crystal-clear water
- Improved coral colour
- Reduced nuisance algae
- Lower phosphate
- Better light penetration
- Reduced water yellowing
- Improved coral polyp extension
These are all positive indicators of effective chemical filtration.
Common Mistakes
Replacing Too Much Media at Once
Changing all chemical media simultaneously can cause sudden changes in water chemistry.
Replacing media gradually often provides greater stability.
Running GFO Without Testing Phosphate
Always test phosphate before adjusting GFO.
Reducing phosphate too aggressively may stress corals.
Poor Water Flow
Chemical media needs adequate water movement to work efficiently.
Avoid tightly packed media bags with minimal flow.
Ignoring Maintenance
Old chemical media eventually becomes exhausted.
Regular replacement ensures consistent performance.
Building a Complete Filtration System
Chemical filtration works best alongside:
- Mechanical filtration
- Biological filtration
- Protein skimming
- Refugiums
- Algae reactors
- UV sterilisers
- Proper water circulation
Each filtration method performs a different role, creating a balanced and stable reef aquarium.
Popular Chemical Filtration Brands
Several manufacturers produce excellent chemical filtration media, including:
- Red Sea
- Seachem
- Nyos
- Tropic Marin
- ATI
- Fauna Marin
- AquaForest
- Rowa
- D-D
- Two Little Fishies
Choosing high-quality media helps ensure consistent performance and reliable results.
Final Thoughts
Chemical filtration is an invaluable part of a complete reef aquarium filtration system. Whether you’re using activated carbon to remove dissolved organics, GFO to control phosphate, Purigen to reduce nitrogenous waste, or specialised resins to target specific contaminants, the right media can significantly improve water quality and create a healthier environment for your fish and corals.
The key is to use chemical filtration strategically alongside mechanical and biological filtration, monitor your water parameters regularly, and replace exhausted media as recommended. With the right approach, you’ll enjoy clearer water, healthier corals, improved nutrient control, and a more stable reef aquarium.
At Charterhouse Aquatics, we stock a comprehensive range of chemical filtration media, media reactors, filter bags, and water testing equipment from leading brands including Red Sea, Seachem, Rowa, Tropic Marin, Nyos, ATI, and AquaForest. Our experienced team is always available to help you choose the ideal filtration media for your reef aquarium.
