What Is a DE Pool Filter? - How Diatomaceous Earth Filters Work

The Short Answer

A DE pool filter uses diatomaceous earth powder - a white mineral powder made from the fossilized remains of microscopic algae called diatoms - to filter pool water down to 2-5 microns.

That is finer than sand filters (20-40 microns) and cartridge filters (10-15 microns). If water clarity is your primary concern, DE is the most effective residential option.

What Is Diatomaceous Earth?

Diatomaceous earth is mined from deposits of fossilized diatoms - single-celled algae that lived in ancient lakes and oceans. When diatoms die, their silica shells remain intact as tiny, intricate lattice structures with microscopic pores.

These pores are what make DE such an effective filter medium. Under a microscope, each grain of pool-grade DE looks like a tiny sponge. As water passes through the powder layer, particles get trapped in those pores.

Pool-grade DE vs food-grade DE: Pool DE is calcined (heat-treated) to produce the correct particle structure for filtration. Food-grade DE has a different structure and does not work the same way in pool filters. They are clearly labeled - use only pool-grade DE in your filter.

Pool-grade DE powder on Amazon

How a DE Filter Works - Step by Step

1. Grids coated in DE: Inside the filter tank, a series of fabric-covered frames (the grids) are coated in a thin, even layer of DE powder. This coating is the actual filter medium.

2. Water enters the tank: Pool water pumped from the skimmer and main drain enters the top of the filter tank.

3. Water passes through the DE layer: As water flows through the DE-coated grids, particles as small as 2-5 microns get trapped in the powder’s microscopic pores.

4. Clean water returns to the pool: Filtered water passes through the grid fabric and out through the center manifold pipe, then back to the pool via the return jets.

5. Pressure rises as grids load: As the DE traps more and more debris, the filter resistance increases and the pressure gauge rises. When pressure is 8-10 PSI above baseline, it is time to backwash.

6. Backwashing removes spent DE: Reversing the water flow dislodges the DE and debris from the grids and flushes it out the backwash line.

7. Fresh DE is added: After every backwash, fresh DE powder must be added through the skimmer to recoat the grids. Without this step, the bare grids cannot filter effectively.

DE vs Sand vs Cartridge - Quick Comparison

For the full breakdown: DE Filter vs Sand Filter vs Cartridge

Who Should Use a DE Filter

DE is a good choice if:

• Water clarity matters more than maintenance simplicity
• You have a high bather load (kids, frequent parties) where finer filtration helps
• Your pool has historically struggled with cloudy water despite correct chemistry
• You are experienced with pool maintenance and comfortable with the extra steps

Consider sand or cartridge instead if:

• You want the lowest-maintenance option
• You have a smaller above-ground pool
• You are new to pool ownership

Key Components of a DE Filter

The tank: Pressure vessel (usually fiberglass) that contains the grid assembly. Rated to 50 PSI.

The grids: Fabric-covered frames, usually 8 per filter, connected to a central manifold. The actual filtration happens in the DE layer on these grids.

The manifold: Central pipe assembly that collects filtered water from all the grids and routes it back to the pool.

The multiport valve: Same design as on a sand filter - positions include Filter, Backwash, Rinse, Recirculate, Waste, and Closed.

The pressure gauge: Monitors filter pressure. Write your clean baseline (right after adding fresh DE) on the housing.

Related Guides

• How Much DE for Pool Filter? - exact DE quantities by filter size
• How to Backwash a DE Filter - complete backwash and recharge procedure
• DE Filter vs Sand Filter vs Cartridge - full comparison
• DE Filters Complete Guide - all DE filter topics