How to Backwash Your DE Pool Filter

Diatomaceous Earth (DE) filters are the most effective pool filters, capable of trapping the smallest of particles.

However, because they are so efficient, they can clog up faster than other systems. If your pool water looks a bit dull or your jets feel weak, it’s likely time for a backwash.

Let’s help you know when its time to backwash your DE filter and how to do it properly.

When Should You Backwash?

Backwashing is not something that needs to be done on a set schedule. If you want to do it monthly, that is fine, but it’s also a waste of DE powder (aka money!).

Instead, let your equipment tell you when it’s struggling.

  • PSI is 25% above normal pressure. At the start of the season, you should get in the habit of remembering your “clean” PSI on the filter. This is the pressure reading when the filter is first turned on and has a full charge of DE. A good rule to follow is to clean out your filter when your pressure is about 25% above normal PSI levels.
  • Sand channeling: If your pool looks cloudy despite having balanced chemicals, the sand may be “channeled,” meaning water is carving paths through the sand rather than being filtered by it.
  • Weak return flow of water: If the water coming out of the wall jets feels like a trickle instead of a strong flow, there is a high chance your filter is holding too much debris.
  • Post-algae shock treatment. If you’ve just finished a shock treatment and have been vacuuming up a dead algae bloom, you should backwash to get that algae out of the filter.

Identifying Your DE Filter Valve Type

There are different types of valves your DE filter can have, and that will determine the backwash process. It either contains a multiport valve or a slide valve.

The multiport valve is a circular dial with a handle that typically contains 6 different positions. These valves offer the most control when it comes to backwashing.

Multiport valve on a pool filter

The slide valve (sometimes referred to as a push-pull valve) is a simpler system that only contains a backwash and filter setting.

Steps to Backwashing Your DE Filter

The backwashing process is pretty straightforward. Follow these simple steps and get your DE filter back to work.

Critical Safety Rule

Always turn off the pool pump before moving the valve handle. Changing valve positions while the pump is running can blow out internal gaskets and cause cracks or expensive leaks

  1. Attach a backwash hose if you have one. If your filter has a waste port, attach a hose so the dirty water can flow farther away from your equipment.
  2. Turn off the pump. You can either shut the main power switch from the pump or, even better, at the circuit breaker box itself.
  3. Set the valve to BACKWASH. This setting reverses water flow, forcing it to go backwards through the grids which cleans them off. Water will shoot out of a waste port.
    • If you have a slide valve, pull the handle UP as far as it will go. This is the backwash position.
  4. Turn the pump back on to start the first cycle. Run the pump for about a minute. If you have a sight glass, run it until the glass is “clear”.
  5. Turn off the pump.
  6. Set the valve to RINSE. This setting removes sediment and dirt caused by the backwash.
  7. Turn the pump back on. Run the pump on RINSE for about 30 seconds.
  8. Turn off the pump.
  9. Repeat steps 3-8 two or three more times. This will guarantee the majority of the heavy dirt and debris has been moved out of the filter.
  10. Turn off the pump.
  11. Set valve to FILTER and turn the pump back on.

For slide valve filters, there is no RINSE position. The backwash process is steps 3 – 5. Once complete, turn the valve back to the filter position.

How Much DE to Add After Backwash

During the backwash process, DE powder gets removed along with dirt and debris. Once complete, you’ll want to add 80% of the original DE amount recommended for your filter.

For example, my filter requires 7.5 lbs. of DE. After backwashing, I add 6 lbs.

Check the manual, your filter’s label, or online for the startup amount of DE.

Add the DE through the skimmer basket. The easiest way would be to mix the powder in a 5-gallon bucket of water, then slowly pour the mix into the skimmer basket.

Now Time to Get Back to Swimming!

Remember, you don’t have to backwash a set amount of times during the swim season. Only do it when its necessary.

Once the season is over, prepare for a complete teardown and cleaning. But for now, have fun in the water!