How to Backwash a DE Filter

a blog by James

If you have a DE filter, backwashing the filter is very important both for the life of your filter as well as the clearness of the water. In this blog, we will go over how to backwash a DE filter. You’ll want to backwash the filter once a day at the beginning if the water is very dirty. Otherwise, you’ll want to backwash the filter every 2-3 weeks throughout the season. You will know its time to backwash the filter when the pressure gauge is around 20-25 psi, but it can vary from filter to filter. The easiest way to tell if its time to backwash your filter, is the pressure coming out of the returns will be very weak.

Once you know you need to backwash the filter, the first step is to make sure there is a discharge hose connected to the multiport if there isn’t hard plumbing. Once you’re set, you’ll want to turn off the pump, move the handle on the multiport to “backwash” and then turn on the pump for about 60 seconds, or until the water clears up. The water should come out a dirty gray color, which is the old DE. Once the water clears up, turn off the pump, move the handle to “rinse” and turn on the pump for about 20 seconds.

After this, turn off the pump, go back to “backwash” and do the same thing until the water is almost clear. Then turn off the pump and “rinse” again for 20 seconds. Most filters will need 2-4 cycles like this to get the old DE out. After the filter is backwashed, it is VERY important that you have more DE to replenish the old DE. Failure to add more DE after the backwash will result in damage to your filter and will most likely lead to a dirty and/or green pool. The DE is added to the skimmer while the pump is running. You’ll want to make sure the handle is moved back to “filter”, then turn on the pump, and then add the DE directly to the skimmer.

Most filters take between 3-6 lbs of DE. Its usually written on the label on the side of the filter. Make sure to empty the skimmer baskets before adding DE and make sure the valve to the skimmer is not turned off, as the filter will not replenish the DE if the skimmers aren’t turned on. If you are still having issues with your pool after backwashing and the pressure on the filter doesn’t go down, you might need to clean your filter, which will be covered in another blog.