DE filters also should be backwashed when gauge reads 8–10 lbs higher than its clean starting pressure.. This involves turning a valve so that the water will flow through the filter backwards, flushing out the dirt, hence the name “backwashing.” DE filters can have either a slide valve or a multiport valve. The multiport valve has multiports on the valve, usually 6 positions:

1. FILTER: This is the normal setting for filtering your pool water and for regular vacuuming.
2. RINSE: Use this setting for 20 seconds after backwashing to rinse tank.
3. RECIRCULATE: Use this if the filter’s broken, at least you’re circulating your pool.
4. BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out.
5. CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position.
6. WASTE/ DRAIN: This setting is used to bypass the filter, but this one sends the water out of the waste pipe (hose), instead of returning it to the pool. It is used to lower pool water level or to vacuum to waste.

A DE filter with a multiport valve

Here are the steps to backwash a DE filter with a multiport valve:

• Shut off pump motor
• Press down on valve handle and rotate valve from FILTER to BACKWASH position
• Roll out any backwash hose or open any waste line valves
• Open air bleeder assembly on filter and turn pump on
• Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly
• After hose fills with water, run for 2-3 minutes or until water runs clear
• Shut off pump motor and move multiport valve handle to RINSE position. Run on rinse for 5-s10 seconds. Shut off pump again, and move handle back to BACKWASH. Turn on pump again until water runs clear. Repeat this 3-4 times, alternating between backwash and rinse to ensure a thorough backwash.
• Shut off pump motor and move multiport valve handle to FILTER position
• Turn pump back on and note lower pressure. Roll up backwash hose
• Add 1 lb DE powder per 10 sq. ft. of filter area. Look on filter tank

And the following are the steps to backwash a DE filter with a slide valve:

• Shut off pump motor and roll out backwash hose (if you have it)
• Twist to unlock plunger T-handle, and pull/ twist plunger upwards 2-3″
• Open air bleeder assembly on filter and turn pump on
• Watch pressure gauge for backpressure (+ 40 PSI) and hose for kinks. Be prepared to shut off pump quickly
• After hose fills with water, run for 1-2 minutes or until water runs clear. Shut off and push handle back down. Turn pump on and run in filter position for 15 seconds and then shut pump off and backwash again for 1 min. Filter again for 15 seconds and another backwash for 30 seconds
• Shut off pump motor and push T-handle back down into locked position
• Turn pump back on and note lower pressure. Roll up backwash hose
• Add 1 lb DE powder per 10 sq. ft. of filter area. Look on filter tank.

A properly sized DE filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashings. A “Filter Run” of less than 4 weeks may indicate grid problems (or sizing problems). Filter grid fabric can become clogged with calcium deposits or oils. After removing the grids from the assembly, you can soak in TSP (trisodium phosphate) and warm water to remove oily deposits. If you have high levels of calcium or other minerals in your pool water, you can soak the grids in a 10% muriatic acid solution for a few minutes followed by a full rinse. TSP soak and rinse will remove mineral deposits such as calcium.