How to Backwash a Pool Filter the Right Way

Maintaining a clean pool is essential for enjoying safe and clear water, and a well-functioning filter plays a key role in that. Backwashing is one of the most effective ways to clean your pool filter, and it doesn't always require taking it apart. In this guide, we'll walk you through the proper steps to backwash a pool filter and explain the best practices to ensure your filter stays in optimal working condition.

What Is Backwashing a Pool Filter?

Backwashing a pool filter involves reversing the flow of water through the filter to dislodge accumulated dirt, debris, and other contaminants. Over time, as water flows through the filter—whether it’s a sand or diatomaceous earth (D.E.) filter—the filter medium (sand or D.E.) traps particles like dirt, oils, and leaves. As this buildup increases, the filter becomes less effective. Backwashing sends water backward through the filter, forcing the debris out through the waste or drain port. This process restores the filter's efficiency and keeps your pool water clean.

How to Backwash a Sand Filter

A sand filter works by trapping debris in the sand as the water flows through it. The sand remains inside the filter, but periodic backwashing is necessary to clean it. Here's how to do it:

Supplies Needed:

• Backwash hose (to direct the dirty water out of the system)

Steps for Backwashing a Sand Filter:

1. Turn off the pool filter system to ensure safety during the process.
2. Attach the backwash hose to the waste or backwash port on the filter.
3. Set the multiport valve to Backwash. This changes the direction of the water flow.
4. Turn the filter system back on and let it run for about a minute or until the water running through the hose becomes clear.
5. Turn off the filter system again.
6. Set the multiport valve to Rinse and turn the system on for about 30 seconds to help settle the sand back into place.
7. Turn off the filter system once more.
8. Return the multiport valve to Filter mode to resume normal operation.

Important: Always ensure the filter system is off before adjusting the multiport valve to avoid damaging the valve or causing leaks.

How to Backwash a D.E. Filter

Diatomaceous earth (D.E.) filters use a fine powder to coat the filter grids, creating a "cake" that helps trap even the smallest particles in the water. Here's how to backwash a D.E. filter:

Supplies Needed:

• Backwash hose
• Diatomaceous earth (D.E.) powder
• One-pound D.E. scoop (or empty one-pound coffee can)

Steps for Backwashing a D.E. Filter:

1. Turn off the pool filter system.
2. Attach the backwash hose to the filter’s waste port.
3. Set the multiport valve to Backwash (or open the backwash gate if using a push/pull valve).
4. Turn the filter system on and allow it to run for about 2 minutes to flush the filter.
5. Turn off the filter system again.
6. Set the multiport valve to Rinse and run the system for about a minute.
7. Turn off the filter system once more.
8. Return the multiport valve to Filter mode to resume normal operation.

Once backwashing is complete, you will need to add new D.E. powder to the filter to restore its ability to filter fine particles effectively.

Steps for Adding D.E. Powder:

1. Prime the pool pump by removing the strainer basket lid, filling it with water, and allowing the pump to run.
2. Mix the D.E. powder with water to create a slurry (thin, creamy solution).
3. Pour the slurry directly into the pool skimmer while the pump is running.
4. Run the pool pump for at least 30 minutes to ensure the D.E. powder is evenly distributed over the filter grids.

Important: As with sand filters, always ensure the multiport valve is not adjusted while the system is running to prevent valve damage.

How Often Should You Backwash a Pool Filter?

The frequency of backwashing depends on several factors, including pool usage, water quality, and the type of filter. A good rule of thumb is to backwash your filter when the pressure gauge reads 10 psi above its normal operating level. If you’re unsure, it’s generally best to backwash when the pressure increases significantly above normal levels to maintain the filter’s performance.

Proper Disposal of Backwash Water

Disposing of the water from a backwash is an important part of the process. Pool backwash water can contain chemicals that are harmful to the environment, so it’s essential to dispose of it correctly. Here are some options for disposal:

• Storm Drains: Some areas allow backwash water to be disposed of in storm drains. Check with your local authorities to see if you need a permit and if any chemical treatments are necessary.
• Plumbing Cleanouts: Directing backwash water into a plumbing cleanout may be an option in some areas. Again, check with local authorities for regulations.
• Dry Wells: In some cases, you may use a dry well to dispose of backwash water, though you’ll need to ensure the system is built to handle it and complies with local laws.

Conclusion

Backwashing is an essential task for maintaining the performance of your pool filter, whether you have a sand or D.E. filter. Following the correct procedures will not only help keep your pool water clean but also extend the life of your filter. Be sure to check your filter’s pressure regularly and backwash when necessary to ensure optimal filtration.

If you’re ever unsure about the specific steps or materials needed, always refer to your filter’s owner’s manual for guidance. Keeping your pool filter in top condition is key to enjoying crystal-clear water all year long!