How to Backwash a Sand Filter (With 6 Easy Steps)

How To Backwash A Sand Filter

Sand filters don’t trap sand. Instead, they use sand to trap large particles as water is pumped through them. This simple filtration mechanism is very easy to maintain but needs to be thoroughly washed every once in a while, to get rid of residue from the sand.

That said, in this article, we will look at the signs that show when a backwash is due and how to backwash your sand filter. Let’s get started.

When to Backwash A Sand Filter

Generally, most people suggest that you should backwash your pool’s sand filter weekly as you test the pool chemicals. However, this is not ideal because the pool is not always in the same condition.

For instance, if you are dealing with high levels of algae or high levels of debris, then you need to clean it more often to prevent clogging.

Well, in such a case, how do you know when to backwash the filter? Here are some few signs to look for.

1. Increase in PSI

Each filter is rated by the manufacturer to perform optimally at a certain pressure, and this is usually given in PSI. As more and more debris pile up and blocks the spaces between the sand particles, it reduces the amount of water passing through and this raises the pressure level inside.

To check this, the filters have pressure gauges, and if you notice that the level is about 8-10 PSI higher than the rated operating pressure, then it is time to do a backwash.

2. A Drop in Flow Rate

This goes hand in hand with an increase in PSI. As the water channels through the sand are blocked by debris, less water penetrates through and this lowers the flow rate.

That said, this can be a bit difficult to measure because the filters and their pumps don’t come with flow rate meters. Therefore, if you want to monitor this, you can install such a meter on the pipeline, just after the filter.

With this, if you spot a drop in the GPM (Gallon Per Minute) output, then it is highly likely that the filter is clogged. The pump and filter system is usually rated at a certain GPM and this should help you determine if there is a drop.

3. A Decrease in Water Clarity

With the sand filter clogged, it won’t be as effective in trapping debris. Therefore, this will result in some cloudiness in the pool, and in the worst-case scenario, you might even spot floating particles.

A better way to check this is by testing for Total Dissolved Solids using your test kit. If it is higher than the required level (about 1500-2000 ppm), then you need to backwash the filter.  

How to Backwash a Sand Filter

When to Backwash A Sand Filter


1. Turn Off the Filter 

Begin by powering off the filter’s pump to stop the flow of water through the sand. This is a protective measure that keeps the valve from getting damaged.

2. Connect the Waste Hose Securely to The Backwash Port 

Attach and fasten the waste hose to the backwash port for directing wastewater either to your drainage system or to the ground. Ensure it is not kinked for continuous water flow.

3. Select the Backwash Function

Mode selection is done using the valve handle and to shift to the backwash function, first depress it to release the selector pointer from the groove on the outer plate. Turn the free handle to the backwash position then release the handle to lock in that position.

4. Turn on The Filter

Power on the pump to backwash the sand. Let it run for about 2 minutes as you observe the sight glass. Once the water becomes clear on this observation window, turn off the pump then proceed to step 5.

5. Rinse the System

What happens after backwashing is that some sand and debris settle in the filter’s plumbing and this needs to be cleared before use.

Move the valve handle setting from “backwash” to “rinse” then turn on the pump to run water through this setting. Once the water becomes clear in the sight glass, turn off the pump. This setting pushes sand back to its compartment and flushes debris outside.

6. Set the Filter Back to the Normal Setting 

Set the handle back to its normal position, which is the filter setting. Turn on the pump then check the pressure level on the pressure gauge. If you have a flow rate meter installed, check the flow rate. Ensure all parameters are within the manufacturer’s operating ratings.

Backwashing Tips

  • Backwashing wastes a lot of water and this is unavoidable. Therefore, you should keep an eye on the sight glass so that you stop the process as soon as the water’s color and quality improve.
  • If your pool is very dirty, you should turn off the filter and use a pool vacuum cleaner instead. This will help to minimize water loss.
  • Do not overdo the backwashing cycles. Sand particles filter more efficiently when they have settled for some time. Therefore, if you backwash more frequently, you will keep disrupting the sand particles’ positioning, which reduces the filter’s efficiency.
  • Always turn off the pump before switching between the different settings using the valve handle. If you don’t do this, you might damage the filtration system.
  • When turning the valve handle for mode selection, always turn in one direction (right or left). Do not turn in the opposite direction as a shortcut to get to the required setting. Turning in both directions can unite the spider gasket, increasing wear and tear.


To sum it up, backwashing a sand filter is a necessary process towards maintaining a clean pool and having an effective filter. Following the steps above will ensure you reset the filter to function at its highest efficiency level.