Mr. Saltwater Tank

Write-Up Wednesday: Filter Socks


A filter sock is a form of mechanical filtration whose purpose is to trap large particles flowing through it. The sock will usually be labeled for the smallest size particle that it will trap e.g. a 200 micron sock will stop particles down to the 200 micron size.

To hold the sock open and to provide a way to secure the sock in a filter sock holder, a plastic ring is built into the top of the sock. If you don’t have a filter sock holder, a filter sock with a drawstring at the top can be used instead.

Filter socks come in two flavors – mesh and felt depending on which material they are made of. The mesh filter socks are easier to clean while felt filter socks trap more particles.

Like any mechanical filter, over time the filter sock will need to be cleaned to keep the trapped particles from breaking down and causing nutrient issues in your tank. And please don’t buy into the terrible advice that rinsing your filter socks will crash your tank as the biological filtration provided by the socks should be minimal compared to the overall biological filtration in your tank!

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Comments for this article (4)

  • Scott says:

    As always, great advise. Thank you very much for conveying this and all information.

  • Bill C says:

    I’m wondering what hole size should be used. I know that 200 is most common, but does that mean it is the best. What is the largest size particle a skimmer pull out? I would think that if a skimmer can pull up to a 199 micron particle then yes 200 is perfect but if a skimmer can only pull particles up to 50 microns then we should be using 50 or 100 micron socks. Any thoughts on matching sock size to the skimmer performance?

  • Bill…skimmers can pull out very, very small particles down the molecule size. These will pass right through a filter sock. No need to try to match your filter socks to your skimmer. Just use the 200 micron sock size and skim away!

  • Bill C says:

    Hey Mark, I think I failed to make my question clear, I’m thinking that the sock could be scaled to pull the particles that were too big for the skimmer. So my question really is where does a skimmer stop pulling particles out of the water column, how big does something have to be for it to be too big for the skimmer to collect and should we just use the sock for these big bits?

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