A DE filter tank contains internal grids (or fingers, depending on design) covered with a fabric septum. When the system is first started or after backwashing, DE powder is added through the skimmer as a slurry. The pump draws this powder onto the grid fabric, where it forms a thin, even coating — the actual filter medium.
As pool water passes through the grids, particles as small as 5 microns (including bacteria and fine algae) become trapped in the irregular microscopic structure of the DE powder. The water that passes through is remarkably clear.
Over time, the DE layer becomes saturated with captured material and filter pressure rises. Backwashing reverses water flow to flush the clogged DE off the grids and out to waste — but the DE goes with it and must be replaced with fresh powder.
| Feature | DE Filter | Sand Filter | Cartridge Filter |
|---|---|---|---|
| Filtration size | 5 microns | 20–40 microns | 10–15 microns |
| Water clarity | Excellent | Good | Very good |
| Maintenance frequency | Monthly backwash + recharge | Monthly backwash | Quarterly clean |
| Annual deep clean | Yes (disassembly) | Yes (media replacement 5–7 yr) | Yes (cartridge replacement) |
| After backwash | Must add new DE | No additional step | Cartridge doesn't backwash |
| Best for | Highest clarity, fine debris | Easy maintenance, large pools | Low water use, moderate clarity |
Never add dry DE powder directly to the pool. It will cloud the water and the fine silica dust can irritate swimmers' eyes and skin. Always mix DE into a slurry first, and always add through the skimmer with the pump running — not directly into the pool.
Once per year (or when backwashing no longer restores normal pressure), the DE filter needs a full disassembly and cleaning:
PoolLens logs your filter pressure readings so you can see exactly when pressure has risen 8–10 psi above baseline and needs backwashing. Log DE recharge dates and annual cleaning events to stay on schedule.
Open PoolLens Free →DE is made from fossilized diatom shells with a porous microscopic structure. Water passing through a DE layer is filtered to 5 microns — capturing bacteria, fine algae, and tiny debris that pass through sand (20–40 microns) and cartridge (10–15 microns) filters.
Mix the required amount of DE powder into a slurry (water + powder in a bucket). With the pump running in "filter" mode, pour the slurry into the skimmer. The pump draws it onto the internal filter grids. Never add dry DE to the pool directly.
When pressure rises 8–10 psi above the clean baseline, typically every 4–8 weeks under normal conditions. Always recharge with fresh DE after backwashing — the old DE powder is washed away and must be replaced. Perform a full disassembly and manual cleaning once per year.
Pros: finest filtration (5 microns), clearest water, excellent for algae treatment. Cons: most maintenance of the three filter types — must recharge DE after each backwash, annual disassembly for deep cleaning, cracked grids cause DE to enter the pool. Best for: pools where water clarity is the top priority.
A cracked or torn filter grid allows DE to pass through the filter into the return flow. Remove the grid assembly, inspect every grid for tears or cracks, and replace any damaged components. This is the most common DE filter problem and requires prompt attention — DE in the pool irritates eyes and skin.