So Many Options — What Actually Works?
Marine shops stock an entire wall of filter media — bags, tubs, pellets — all promising crystal-clear water. But what works, what's a waste of money, and what could cause problems if used incorrectly?
Activated Carbon
Carbon adsorbs dissolved organics, yellowing compounds, coral warfare chemicals (allelopathy), and medication residues. The result is clearer water with better light penetration.
When to use it:
- Continuously on mixed reef tanks
- After medicating a quarantine tank
- After suspected contamination (aerosols, paint fumes, etc.)
Popular options: Seachem Matrix Carbon (£12–15/500ml), D-D Rowacarbon (£10–14/500ml), Bulk ROX 0.8 (~£20/500ml).
Run about 50–100ml per 100L of water volume. Replace every 3–4 weeks — saturated carbon stops working. Important: cheap carbon can leach phosphates. Always rinse in RODI water first and stick to reef-grade brands.
GFO (Granular Ferric Oxide)
GFO binds dissolved phosphate, pulling PO4 out of the water column. Essential for battling high phosphates or nuisance algae.
Popular options: D-D Rowaphos (~£15–20/500ml), Two Little Fishies Phosban, Seachem PhosGuard.
Critical: GFO can strip phosphate too fast. Rapid PO4 drops stress corals — SPS especially. Start with half the recommended dose and test every few days. Run 50–100ml per 100L, replacing every 4–8 weeks.
Seachem Purigen
A synthetic adsorbent that removes nitrogenous organics before they enter the nitrogen cycle. Unlike carbon, Purigen can be regenerated with a bleach soak — one bag can last years. About £12–15 for 100ml, making it excellent long-term value.
Bio Pellets
Solid carbon dosing that feeds bacteria which consume nitrate and phosphate. The bacteria-laden water gets exported via the protein skimmer. These require a strong skimmer, take 4–8 weeks to show results, and can cause bacterial blooms if overdosed. Generally best reserved for tanks where water changes plus GFO aren't keeping nutrients in check.
A Common Combo
For a typical UK mixed reef, many reefers run:
- Carbon — continuously, replaced monthly
- GFO — continuously or as needed based on PO4 readings
- Purigen — continuously, regenerated when exhausted
Run media in a reactor for best results, or in mesh bags in a high-flow sump area as a simpler alternative.
Browse filtration equipment from UK sellers — media reactors and bulk filter media are often available from reefers upgrading their setups.
What filter media combo is working on your tank? Running anything unusual?
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