Pentair Quad D.E. Filter: Pressure Remains High After Backwash

Backwashing a Quad D.E. filter flushes the debris-loaded diatomaceous earth off the cartridge surfaces and out the waste line. When pressure fails to drop back to the clean baseline after a backwash cycle, the cartridges are still loaded — either because one backwash wasn't enough, or because the cartridge fabric itself has become embedded with minerals, oils, or scale that water alone can't clear. The Quad D.E. manual establishes a clear three-step escalation for this problem: backwash again, then manually clean the cartridges, then soak them, and finally replace them if nothing else works.

What "High Pressure" Means on a D.E. Filter

The clean operating pressure for a Quad D.E. filter is the baseline reading taken immediately after startup with fresh DE applied. The manual's max working pressure is 50 psi. In practice, most systems run at 10–20 psi clean. A reading approximately 10 psi above that baseline indicates it's time to backwash. If the gauge returns to within a few psi of baseline after backwash, the filter is working correctly. If it does not drop — or drops only slightly — work through the steps below.

Step 1: Backwash Again

The manual's first corrective action is simply to backwash a second time. A single backwash cycle may not fully purge the DE and debris from all four cartridge surfaces, especially if the filter was heavily loaded. Run a complete second backwash cycle per the manual procedure, then restart and check the pressure gauge. If pressure returns to baseline, re-coat the cartridges with the correct amount of DE and resume normal operation.

Important: DE must be re-applied after every backwash. Failing to re-coat leaves the bare cartridge fabric exposed to pool debris, which directly contacts and blinds the fabric weave.

Step 2: Manually Clean the Cartridges

If pressure remains elevated after multiple backwash cycles, the manual directs you to manually clean the cartridges. Follow this sequence exactly:

1. Shut off the pump at the circuit breaker.
2. Open the Manual Air Relief Valve on top of the filter. Wait until all pressure has been relieved and the gauge reads zero.
3. Disassemble the filter following the "Disassembling the Filter" instructions in the manual — remove the clamp nut (P/N 198098z), lift the lid, and set it aside.
4. Remove all four cartridges from between the top manifold and bottom manifolds.
5. Rinse each cartridge thoroughly with a garden hose. Spray along the pleats from top to bottom, working around the full circumference of each cartridge. Do not use a pressure washer — high pressure can damage the pleat fabric.
6. Inspect each cartridge for tears, holes, or visible damage while cleaning.
7. Reinstall the cartridges, ensuring each is seated vertically and properly secured between the top manifold and bottom manifolds.
8. Reassemble the filter following the "Reassembling the Filter" instructions in the manual.
9. Re-coat all four cartridges with the correct amount of diatomaceous earth per the manual's "Coating Cartridges with Diatomaceous Earth" section.
10. Start the pump and check the pressure gauge.

Step 3: Tablet Soak the Cartridges

If manual hosing does not restore normal pressure, the cartridge fibers have absorbed oils, calcium deposits, or other minerals that water cannot remove. The manual calls for soaking the cartridges in a commercial filter cleaner tablet solution:

1. Remove the cartridges as described in Step 2.
2. Prepare a soak solution using a commercial filter cleaning tablet or liquid product per the product manufacturer's instructions.
3. Submerge the cartridges fully and soak for the time recommended by the product (typically several hours to overnight).
4. Rinse each cartridge thoroughly with fresh water after soaking — residual cleaner in the pool is a chemistry problem.
5. Reinstall, reassemble, and re-coat with DE.
6. Run the filter and check pressure.

Step 4: Replace the Cartridges

If pressure remains elevated after soaking, the cartridges are at end of life. The manual directs you to replace them using the correct replacement P/N for your model:

After installing new cartridges, reassemble the filter per the manual and re-coat with the full recommended DE charge before starting the pump.

Related Guides

• Quad D.E. Filter: Diatomaceous Earth Entering the Pool
• Quad D.E. Filter: Filter Leaks at Startup
• Quad D.E. Filter: Short Filtering Cycles — Pressure Rising Too Fast
• Quad D.E. Filter: Pressure Drops on the Gauge