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<\/figure>\n\n\n\nSand, DE, and cartridge filters each ask for something different \u2014 and sand filters are picky about the media, covered in our guide to the best sand for a pool filter<\/a>. Treat them the same and you’ll either damage equipment or send a cloud of debris straight back into your pool.<\/p>\n\n\n\n This is the one most people picture when they hear backwash. You’re reversing the flow of water through the sand bed to flush out everything it’s been catching for the past few weeks \u2014 and while you’re thinking about flow, aiming your pool return jets correctly for circulation<\/a> decides how well the filtered water actually circulates.<\/p>\n\n\n\n Watch the pressure gauge. When it climbs 8 to 10 PSI above your clean starting pressure, it’s time. <\/p>\n\n\n\n Backwashing a sand filter that doesn’t need it actually makes it work worse \u2014 and backwashing is no substitute for changing the sand in a pool filter on schedule<\/a>. A slightly dirty sand bed filters better than a perfectly clean one because the trapped debris helps catch finer particles.<\/p>\n\n\n\n Your pool will lose a few hundred gallons every time you do this, and you’ll need to top the pool back up afterward and rebalance your chemistry. <\/p>\n\n\n\n If you’re not sure exactly how much water you just sent down the waste line, the pool volume calculator<\/a> is worth bookmarking. Knowing your true gallonage matters more after a backwash than at almost any other time, because every chemical adjustment you’re about to make depends on it.<\/p>\n\n\n\n DE filters have a multiport valve too, and the backwash procedure looks almost identical to a sand filter on the surface. <\/p>\n\n\n\n That’s where the similarity ends.<\/p>\n\n\n\n After you finish backwashing, you have to add fresh DE powder back into the system. The grids inside need a coating of diatomaceous earth to actually filter anything.<\/p>\n\n\n\n Without it, you’re just pumping water through bare fabric grids, which clogs them with fine debris and shortens their life considerably.<\/p>\n\n\n\n How much DE? <\/p>\n\n\n\n Here’s something the manuals don’t emphasize enough: DE filters need to be opened and manually cleaned a couple of times a year, regardless of how diligent you are with backwashing. <\/p>\n\n\n\n Old DE cakes onto the grids in patches that water flow alone won’t dislodge. If your pressure refuses to drop back down after a proper backwash and recharge, that’s your sign.<\/p>\n\n\n\n One thing worth checking if you’ve inherited a pool or recently switched filter types: make sure the DE filter you have is actually sized correctly for your pool.<\/strong> <\/p>\n\n\n\n An undersized filter will need backwashing twice as often and never quite catch up. The pool filter size calculator<\/a> gives you the surface area you should be running based on your pool’s volume and turnover rate.<\/p>\n\n\n\n Cartridge filters don’t backwash. <\/p>\n\n\n\n This trips people up constantly. There’s no multiport valve, no waste line, nothing to reverse.<\/p>\n\n\n\n When the pressure climbs 8 to 10 PSI above clean, you shut down the pump, open the housing, and physically remove the cartridges to hose them off.<\/p>\n\n\n\n Use a garden hose with a regular nozzle, not a pressure washer. <\/p>\n\n\n\n A neglected cartridge starts filtering poorly long before it looks bad. By the time the pleats are visibly grey, you’ve been swimming in water that’s been doing a mediocre job for months.<\/p>\n\n\n\n Cartridges typically last two to three seasons with proper care. Skip the deep cleans, and you’ll be buying new ones every year, which adds up fast on larger systems that use four cartridges at a time.<\/p>\n\n\n\n Whatever filter you have, the chemistry shifts the moment you finish. <\/p>\n\n\n\n Sand and DE filters send hundreds of gallons of treated water out the waste line, which means your chlorine<\/a>, your stabilizer, and your salt (if you have a saltwater system) all just dropped. <\/p>\n\n\n\n Cartridge cleaning displaces less water but still disturbs things.<\/p>\n\n\n\n Test your water before you do anything else. Then refill, and dose based on the new volume \u2014 not what you remember adding last time. <\/p>\n\n\n\n For saltwater pools, especially, this is where people get into trouble; adding salt by guesswork after a heavy backwash season is how you end up either corroding equipment or running the generator at full tilt with nothing to convert. <\/p>\n\n\n\n The pool salt calculator<\/a> takes the math out of it once you’ve tested.<\/p>\n\n\n\nSand Filters<\/h2>\n\n\n\n
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DE Filters<\/h2>\n\n\n\n
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Cartridge Filters<\/h2>\n\n\n\n
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After Any Backwash or Cleaning<\/h2>\n\n\n\n