How to backwash a pool filter

If there’s pressure built up in your filter or the water’s not flowing well in your pool, it’s time to backwash. Backwashing is a necessary part of sand filter and DE filter maintenance and doing it the right way will save you from losing water or damaging your equipment.

What is backwashing

First, what is backwashing and when should you do it? As pool water passes through your filter, it leaves behind dirt, oils and other debris which are collected in the filter medium. In this case, sand or DE powder. Over time as the water flows through that filter medium will become clogged and that reduces your filter’s effectiveness and that’s when it’s time to backwash. When you backwash, you’re sending water backward through your filter and out your filter’s waste or drain port and this forces all the debris caught in the filter medium to dislodge and clear out.

When should you backwash?

So when should you backwash your pool filter? You should backwash your filter when your filter pressure rises 10 PSI over normal running pressure or if you notice poor flow from your return jet. Take note of your pressure gauge reading when you first set up your filter or right after you backwash, that’s your normal operating filter pressure. When that pressure gauge reads 10 PSI or more above normal, it’s time to backwash. 

Backwashing generally works the same way across filters, but the process changes slightly depending on whether you have a multi-port valve, a push-pull valve, a sand filter, or a DE filter. Now let’s start with how to backwash a sand filter with a multi-port valve. Before you begin, you’ll need a backwash hose. Luckily, this is the only extra equipment you’ll need to backwash your sand filter and make sure you never turn the multiport valve handle while the pool filter is on and running. This could cause the rubber diverter gasket inside the valve to become loose or break.

How to backwash your pool filters

One, turn the filter system off, then remove the skimmer basket, especially if it’s full of debris. Two, attach a backwash hose to your filter’s waste or backwash port. Three, turn your multi-port valve to backwash. Then turn your filter system back on. Water should be flowing out the backwash port and through the hose. Four, let the water run for 30 seconds to one minute or until the water runs clear. Check the clarity coming out of the end of your backwash hose or check your filter site glass if you have one. Five, turn the filter system off and then turn the multi-port valve to rinse. Six, turn the filter system back on and rinse the filter for about 30 seconds. Seven, turn the filter system off. Turn the multiport valve to filter and turn the system back on when you’re ready to run your pool.

Backwash Tips

If you have a smaller filter, like an Intex sand filter, you may want to do your backwashing in rounds. Backwash for one minute and then rinse for one minute. Repeat this cycle three rounds to avoid blowing anything back into the pool. 

How to Backwash DE Filter

Now here’s how to backwash a DE filter. Before you get started, you’ll need one, a backwash hose. Two, diatomaceous earth powder. This attaches to the DE grids inside the filter, creating a DE cake and this cake along with the filter grids inside helps filter out fine particles in your pool water. And the last time you will need is, a one-pound plastic scooper for scooping DE powder.

So how much DE powder will you need? Backwashing won’t remove all the DE powder in your filter so you only need to add about 80% of the amount that you would for a new filter. Most standard-sized DE filters need about three to four pounds of DE powder replaced during backwashing. Since DE powder is measured in pounds, a one pound plastic scooper is helpful for easy measuring. Here’s how to backwash a DE filter with a multi-port or push-pull valve. Remember, never turn the multiport valve handle or the push-pull valve handles while the pool filter is on and running. It can cause the rubber diverter gasket inside the valve to become loose or break.

One, turn off the filter system. Then connect the backwash hose to the filter’s waste port. Two, if you have a multi-port valve set it to backwash. If you have a push-pull valve, open the backwash gate. You can do this by turning the valve to open and pulling up the handle. Three, turn the filter system back on and let it run for one to two minutes. Water should be flowing out the backwash hose. Four, turn the filter system off. Then return the multi-port valve to rinse. Five, turn the system back on and let it run for about another minute. Six, turn the filter system off. If you have a multi-port valve set it to filter. If you have a push-pull valve, press down on the handle and turn it back to lock. Seven, turn the system back on. Make sure the pump is primed and running before adding DE powder.

If it’s not primed, turn the pump off, remove the lid and fill the pump basket full of water with a hose. If you need help with this step, be sure to check out our other video on how to prime your pool pump. Measure out your DE powder. You’ll be adding this directly to your skimmer so make sure that the pump is running. Remove the skimmer lid and the skimmer basket then add one scoop of DE powder at a time. You should see the powder disappear as it’s pulled towards your filter. Nine, run your pool pump for at least 30 minutes to allow DE to distribute evenly over the filter grids. If backwashing your filter isn’t solving your filter problems, it might be time to change your filter medium. You want to change your sand in your sand filter or the grids in your DE filter every four to five years.