Can You Put DE in a Sand Filter to Improve Filtration?

Sand filters, as far as you’ve always known, are intended for sand. It’s in the name. Yet you’ve heard that you can increase the performance of the filter by adding DE to it? Is it okay to use some DE?

You can add a little DE in a sand filter without ruining it. The DE will filter particles down to three microns, improving the filtration temporality. Backwash first, then add the DE. Add between one and three cups of DE.

This guide to using DE in a sand filter will answer all your most burning questions on the topic, such as whether DE filtrates better than sand, how much DE you should use, and whether DE can clog up the sand filter. Make sure you keep reading, as there’s lots of great information to come!

Powder Diatomaceous Earth (D.E.) for DE Filters
Picture shows Diatomaceous Earth or D.E.

Can You Add DE to a Sand Filter?

A word of warning before we start. Sand filters are designed to use sand and not DE. If you do decide to try this, you do so at your own risk. With that out of the way, let’s get on with it.

We’ve discussed sand filters extensively on the blog, especially recently. To recap, sand filters receive unfiltered water towards the top. The water enters the filter bed where the sand sits. The sand in the filter bed will retain dirt and particles so the water that exits comes out cleaner.

Adding a small amount of diatomaceous earth to the sand in a sand filter is a popular alternative among swimming pool owners. Diatomaceous earth–or DE as we’ll call it moving forward–is a type of sedimentary rock comprised of diatoms.

Diatoms are aquatic creatures. In the case of DE, the diatoms are fossilized.

Well that’s great but can you add DE to a sand filter without causing issues?

It is OK to add DE to a sand filter and in most cases will not cause any problems with the filter. The benefits are improved filtering of fine particles and much clearer pool water.

If you’re looking for the best filtering performance, you may consider switching to a DE filter. You can read more about DE filters here: What is a Diatomaceous Earth (DE) Pool Filter?

Will Adding DE Improve Sand Filter Filtration?

Adding a small amount, ¼ to 2 cups of DE will improve the filtration performance of a pool sand filter.

One of the reasons that pool owners decide to make the shift from sand to DE in their sand filters is for better filtration. But the problem is they take a lot more work to maintain.

Sand filters take a lot less maintenance. But the sand in sand filters doesn’t filtrate particles down to very small sizes. The filter will latch onto particles between 20 and 30 microns. DE will filter much finer particles leaving the water clearer.

Beautiful Swimming Pool
Expect improved filtration and clear water like this when adding DE to a sand filter.

Now, we’re not trying to make that sound like these are huge particles. They aren’t. Most clumps of dirt, dust or fine sediment shouldn’t get through.

But DE can filter to a finer degree than sand can though. With DE in your sand filter, now you can be confident the filter is catching particles between one and three microns.

This opens the amount of pool debris your filter can catch by a considerable margin. Spider webs are two to three microns, skin flakes are between 0.5 and 10 microns, and fine silt is eight to 13 microns according to the Engineering Toolbox.

These messes are all things your sand filter cannot pick up with sand in the filtration bed. By adding a little DE, you can ensure your pool is that much cleaner.

What Problems Will DE in a Sand Filter Cause?

So now you know your sand filter will have improved filtration by adding DE to it, you think you might change add some DE today (we’ll tell you how a little later).

Not so fast. While many pool owners can attest to a cleaner pool after using DE in their sand filters, it’s not all roses and rainbows.

Whilst many pool owners have reported excellent success adding DE. There are some potential downsides that could occur by using diatomaceous earth in a sand filter.

Increased Filter Pressure

Sand filters are designed to use sand as the filter media. Using the correct grade of sand produces a predictable amount of pressure inside the filter. The filter is designed for it.

When you add DE to a sand filter, the pressure in the filter will increase. Since you’re effectively making it harder for water to pass through it, the pressure rises. And this can be dangerous if the increase is too big.

Sand filters have exploded in the past, causing fatal injuries. Mostly due to the combination of faulty fasteners and excessive pressure. That’s why you must be very careful.

The key to preventing dangerous pressure when using DE in a sand filter is to add a very small amount at a time. About a quarter of a cup is good.

Then you’ll need to monitor the pressure carefully. It can rise unpredictably. If it does start rising too high, shut off the pump. Then you’ll need to backwash your filter to remove some of the DE and bring the pressure back down.

Possible Clumping

There have been some reported instances of sand clumping together but it doesn’t seem common and most pool owners report great results.

The DE and the sand can combine when moistened by the pool water and become this clumpy mess.

Now that mucked up mixed media cannot filter much of anything. The pool water will still travel through your sand filter, but it won’t come out any cleaner.

It can take a while for you to notice something is wrong, such as when your pool is cloudy or just won’t clean no matter how much you run the sand filter. Then, when you power the filter down and open it up, you’re greeted with DE powder and sand stuck together and making a mess.

DE Powder in the Pool

In some instances, rather than stay in the sand filter, the DE powder can travel straight through your filter and enter your swimming pool instead. There, it will sink to the bottom, contributing a gritty feel.  You’ll have to vacuum your pool using the “waste” setting to clear the DE on the pool floor.

Can You Ruin or Stuff Up Your Sand Filter by Adding DE?

One of my life’s rules is to never say “never”.

It’s very unlikely you will ruin your sand filter by adding DE to it. If by chance you do notice an issue, it will likely be an unwanted pressure increase. In most cases, backwashing will solve this. It’s important to monitor the pressure as you don’t want the pressure going higher than the filter was designed for. That would be dangerous.

The worst thing that could happen is that you could need to replace the sand and clean out the filter. But that’s unlikely. 

How Much DE to Add to a Sand Filter?

Part of preventing excessive pressure in your sand filter is limiting the amount you use. A little can go a long way.

Small sand filters up to one cup of DE
Mid-sized sand filtersup to two cups of DE
Large sand filtersup to three cups of DE

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How to Add DE to a Sand Filter

As promised, let’s review the steps to add DE powder to your sand filter. This will allow the process to go smoothly, as it’s quite a deal more detailed than simply pouring the powder into the filter and hoping for the best.

Here’s what you do.

1. Backwash the sand filter

Begin by backwashing your sand filter. This entails you powering down the pool pump first. Next, adjust the filter valve handle (multiport valve) until it’s set to “backwash.”

Shows what backwashing is and how it works. The image on the left demonstrates regular filtering, the image on the right shows what happens when you backwash your pool.
Backwashing Vs Regular filtering

Now you can run the pump again, backwashing incrementally for up to two minutes. After that time elapses, turn the pump off yet again.

Adjust your filter valve handle, this time turning it to the “rinse” setting. Lock the handle, run the rinse for a minute, and turn the pump off. Set the filter valve to the “filter” setting and turn the pump back on, leaving it running.

We have a full are on backwashing here: How to Backwash Your Pool

2. Note the Filter Pressure

Take a note of the filter pressure. This is to help you figure out how much DE to add to your sand filter.

3. Prepare the DE

Now you can begin to prepare your sand filter for the DE. Grab a bucket that can hold at least a gallon of water. Fill the bucket nearly all the way to the top, leaving an inch of space.

Add the DE powder to the bucket. For that much water, you’d need a ¼ cup of DE.

4. Add the DE to the Skimmer Box

Take your skimmer cover off. Your pump should already be on, so if it isn’t, please turn it on now.

Gradually begin adding the water and DE powder into the skimmer until the bucket is empty. Then you can put the skimmer cover back on.

5. Slowly Add DE Until 1 PSI Increase Achieved

After three minutes, read your pool’s pressure gauge. Repeat steps 3 and 4. That is, keep adding more DE, but only ¼ of a cup at a time until the filter pressure has been increased.

The goal is to get the pressure reading at least 1 PSI over what the pool’s natural pressure is when clean. This might entail you adding more DE powder, but you should still only do so in ¼-cup increments. 

Warning: DE is classified as a Group 3 carcinogen. At present there are no final conclusions reached as to the extent of this. Take precautions when using DE and do not breathe it in.

Conclusion

Putting diatomaceous earth or DE in a sand filter is an alternative to buying and maintaining a costly DE filter. The DE powder will improve the filtering ability of your sand filter when used in moderation.

If you do decide to give it a go, add ¼ of a cup at a time and up to 2-3 cups in total. Watch the pressure gauge carefully and make sure the pressure doesn’t go up by more than 1 or 2 PSI.  

If you’ve been considering putting DE in your sand filter, we hope the information in this guide helps you decide!

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