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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Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.
How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.
What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.
How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.
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