Change filter socks every 3–5 days, or sooner if they clog or discolour. Bulk Reef Supply warns that a clogged sock does more harm than none, because the trapped waste rots and adds nitrate and phosphate back to the water. Floss works the same way and is cheaper, but you throw it away rather than washing it.
Why change them so often
A sock catches waste so you can take it out of the tank. But the waste keeps breaking down while it sits there. Bulk Reef Supply says a clogged sock left in place releases nitrate and phosphate, doing more harm than no sock at all.
If nitrate is a problem, change them more often. Bulk Reef Supply’s nitrate guide suggests every 1–3 days. See high nitrate.
Socks or floss?
Both catch particles. Socks fit a holder in the sump and can be washed and reused, so they cost more upfront but less over time. Floss is cheap, fits most filter boxes, and is thrown away when dirty. Automatic fleece rollers advance on their own and need changing less often, but cost more to buy.
Washing socks
Bulk Reef Supply’s method: turn them inside out, run an empty hot rinse, then a hot cycle with 2–3 capfuls of fragrance-free bleach and no detergent. Air dry for at least two full days. If you can still smell bleach, soak them in dechlorinator before use.
It suggests keeping at least 3–4 spares, so there’s always a clean one ready.
Make it a habit
Socks are easy to forget until the bypass is overflowing. A repeating task every few days, plus a weekly wash, keeps them working.
Common questions
How often should I change filter socks?
Every 3–5 days, Bulk Reef Supply says, or sooner if they clog.
Can I wash filter socks in the washing machine?
Yes, inside out, with fragrance-free bleach and no detergent. Dry them fully.
Do I need filter socks at all?
Not every tank uses them. If you do, change them often.
Sources and limits
Last checked 13 October 2026. Follow your equipment maker’s own instructions where they differ from this guide.
Keep going
Add a filter sock routine · Free Reef Companion · All calculators