Updated 2026
The best filter media is the one that solves a specific, measured problem. A reef tank normally relies first on live rock, stable husbandry, sensible stocking, and regular water changes. Mechanical, chemical, and biological media can strengthen that foundation, but piling every option into the filter can create extra maintenance or strip nutrients too quickly.
Affiliate disclosure: Some links below are affiliate links. If you buy through them, I may earn a commission at no extra cost to you. I only recommend a product when it fits the job described.
Think of the three jobs separately: mechanical media catches particles, chemical media binds selected dissolved compounds, and biological media provides surface area for nitrifying bacteria. Before adding chemical media, test the relevant parameter and compare it with my recommended saltwater parameters.
- Mechanical media: rinse or replace it before trapped waste breaks down.
- GFO and other phosphate media: use a conservative amount only when phosphate testing shows a need; rapid nutrient reduction can stress a reef.
- Activated carbon: useful for water clarity, odors, and removing many dissolved organics; rinse it thoroughly and follow the manufacturer’s amount and replacement directions.
- Biological media: useful when rock surface area is limited, but never clean all of it at once or rinse it in chlorinated tap water.
Media bags work well when water is forced through them without bypass. Reactors can improve contact for carbon or GFO, but they also require careful flow, leak checks, and regular maintenance. Start small, test again, and change only one variable at a time.
5. Mesh Filter Bags
Reusable mesh media bags are a simple way to hold loose carbon, GFO, or other granular media without adding a reactor. Choose a mesh size fine enough to contain the media, leave room for water to move through it, and secure the drawstring so granules cannot escape.
Place the bag where water is directed through it—not resting in a low-flow corner of the sump. Rinse the filled bag with purified water before use, inspect it when you service the filter, and clean or replace the bag when flow is restricted. The 4 × 8-inch size is convenient for many small systems, but media amount should follow the product directions rather than tank size alone.
4. GFO
Granular ferric oxide (GFO) binds phosphate. It can be helpful when a reliable phosphate test confirms a level you want to reduce, but it is not a substitute for correcting excess feeding, trapped detritus, exhausted source-water filters, or other nutrient inputs.
Start below the manufacturer’s maximum dose, keep flow gentle enough that the surface only barely moves in a reactor, and retest before adding more. Lowering phosphate too quickly can stress corals and destabilize a reef. Standard GFO is usually the sensible starting point; high-capacity GFO packs more binding capacity into less space, but that is not automatically better for a beginner.
3. Poly-Filter
Poly-Filter is a cut-to-fit Poly-Bio-Marine pad that combines particle capture with adsorption. It is most useful as a problem-solving or polishing tool—for example after a suspected contaminant or when removing residual medication from an appropriate system—not as a reason to skip diagnosis or water changes.
The pad changes color as it loads, but color alone is not a complete water test. Follow the manufacturer’s instructions, provide good flow through the material, and replace it when exhausted or when flow is restricted. If livestock show distress or you suspect a toxin, begin with aeration and a substantial water change while you identify the source.
2. Ceramic Bio Media
Ceramic biomedia provides additional surface area for nitrifying bacteria. It can be useful in tanks with limited porous rock, compact all-in-one filtration chambers, or systems that need removable seeded media for a quarantine or hospital tank.
Biomedia does not make overstocking safe, and it does not guarantee meaningful nitrate removal. Its most dependable role is supporting the bacteria that convert ammonia to nitrite and then nitrate. Keep it in oxygenated flow, swish it gently in discarded saltwater when detritus accumulates, and never clean or replace all of it at once. Avoid chlorinated tap water, which can damage the bacterial population.
1. Activated Carbon
Activated carbon adsorbs many dissolved organic compounds that discolor water or create odors, and it can help remove many medications after treatment when the medication label calls for it. ROX 0.8 is a high-performance, low-dust carbon, so a small measured amount can be effective.
Rinse carbon thoroughly until the rinse water is clear, contain it in a fine mesh bag or run it in a reactor with gentle flow, and replace it according to the manufacturer’s directions or when its effect is exhausted. More is not always better. Carbon does not remove every contaminant, and it should support—not replace—source control, testing, and routine maintenance.
