Here’s How To Backwash A Sand Filter In 7 Easy Steps


In today’s post you’re going to learn how to backwash your sand filter … in 7 EASY steps.

Sand filters are pretty easy to maintain, but once in a while, you do need to clean them by reversing the water flow to send clean pool water through it to rinse off the sand, expelling the dirty water via the waste line into the drain or ground. 

Simple enough, right?

When should I backwash my sand filter?

Some experts say that you should backwash it at least once a week and some say to only clean it when it is dirty.

I personally don’t think it hurts to take care of it once a week when you are checking your pool chemicals, but there are certainly instances when you should clean it more often like when you’re battling algae, after a storm and when you see obvious signs that it’s dirty.

And here are a few ways to know if your sand filter is dirty:

1. Increase in PSI

PSI (pounds per square inch) is the measure of pressure your filter is operating on.

Your sand filter should have a pressure gauge to see this number clearly and all pool filters are different. Find out what the baseline pressure for your filter is and check it every time you check your chemistry levels. 

The rule of thumb here is that when your PSI reads 8-10 lbs over its normal baseline, it’s probably time to backwash.

2. Drop in flow rate

A drop in your filter’s normal flow rate, or GPM (gallons per minute), is another way to know your filter might be dirty.

Each filter and pump system has its own normal GPM, which you should be able to find out from your manufacturer’s guide or a quick Google search for your particular model. 

This is a little harder to measure because a lot of pools don’t have pool flow meters installed.

You can install one into your plumbing line if you want the accuracy of knowing, and it’s not a bad idea at all.

However, if the flow rate is dropping, you’ll likely experience an increase in PSI and cloudy water as well, so you can usually just go by those two indicators to know when it’s time to backwash.

3. Decrease in water clarity

If you notice your pool water getting a little cloudy or see debris floating in it that the filter doesn’t seem to be removing, it could mean the filter isn’t working as well as it should. You’ll also notice high TDS (total dissolved solids) levels when you test your chemistry levels if this is the case.

Both of these things could mean you have a dirty filter and need to backwash it ASAP.

How to backwash your pool sand filter

Backwashing is an easy process, but you do want to make sure you follow the steps correctly to get it as clean as possible.

  • 1Turn the pool filter system off.
  • 2Attach your pool hose to the backwash port on your sand filter.
  • 3Select the “Backwash” position on your multiport valve handle.
  • 4Turn the pool filter system on and allow it to rush out of the backwash port and through the backwash hose for two minutes or so until the water in the sight glass runs clear.
  • 5Turn the filter off again and set your multiport filter valve to the “Rinse” position.
  • 6Turn the pool filter system back on and allow it to run for a minute or so.
  • 7Turn the pool pump off and switch the multiport valve to its original setting (usually the “Filter” position).

That’s it!

Your pool water should be crystal clear and ready to swim in again!

If you’re still noticing some of those signs of a dirty sand filter, you may need to re-evaluate the situation.

Check all your chemicals to make sure something else isn’t off, like calcium hardness or pH balance.

If you can’t seem to get those corrected and your sand filter doesn’t seem to be working as well as it used to, it may be in need of a repair.

But if everything is running correctly, backwashing your filter and keeping your chemicals balanced should keep you in the pool all summer without any worries.

Let us know if you have any questions!

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