Chemical filtration is the third filter stage and removes molecules that mechanical + biological can't catch. Activated carbon (GAC): removes organic compounds (DOC), tannins, medications, odors. Replace every 3-4 weeks - exhausted carbon stops adsorbing. GFO (Granular Ferric Oxide): removes phosphate (PO4). Place in fluidized media reactor. Replace when media stops decreasing PO4 levels. Purigen (Seachem): regenerable synthetic adsorber - removes DOCs, tannins, ammonia. Soak in 1:1 bleach/water 24h, dechlorinate thoroughly to regenerate. Cuprisorb: removes residual copper after QT treatment. Caveat: chemical filtration removes medications too - always remove during dosing.
Reviewed by the Fast Aquatics husbandry team · Updated May 2026
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