Filter socks polish water in sumped reef + freshwater systems. Common micron ratings: 100 micron (catches large debris, polishes water hardest), 200 micron (general use, replace 7-10 days), 300 micron (catches less, allows pods + some flow). Maintenance: replace every 5-7 days. Old socks become filthy + decay into nitrate. Wash in washing machine on hot, no detergent (or just discard $2 socks). Brands: Eshopps Filter Sock, BRS Bulk Reef Supply ($5-10 each), 200-micron felt filter cloth (cheap). Alternatives: 1) filter rollers (Theiling, Red Sea ReefMat) - automate sock replacement. 2) sponge in sock holder. 3) skip filter sock in low-bioload sumps. Pros: dramatically clearer water, removes detritus before decay. Cons: daily monitoring + frequent replacement, biological hazard if neglected.
Reviewed by the Fast Aquatics husbandry team · Updated May 2026
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