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Unlike sand filters, frequent backwashing of DE filters does not affect the filtration rate. However, it does create extra work and expense for service techs. Similarly, the backwash process should only take three minutes; however, the cycle should be broken down into a one-minute backwash, then a one-minute filtration for three separate cycles (making sure to shut the pump off each time when switching between backwash and filtration).
This procedure helps to separate the DE coating from the grids so it can be removed from the filter. These filters should be backwashed at the same 69 kPa (10 psi) increase over normal operating pressure as any other filtration media. The filter should be torn down, cleaned, and degreased at least twice a year, too. Body lotions and sunscreen collect on the grid material and cannot be removed via backwashing. A degreasing agent should be used to complete the filter maintenance process. It is important to note, muriatic acid will permanently lock the oils and lotions into the grid material and, is therefore, not recommended.
When recharging a DE filter, the manufacturer’s recommendation should be followed as to the amount of media to use to charge the filter. The proper method is to use a 19-L (5-gal) bucket to mix the DE and water together to create a slurry. Once mixed, it should be poured slowly into the skimmer while the pump is running. This will ensure the grids or elements are properly coated from top to bottom.
If a service tech finds a backwash valve on a cartridge filter, something has gone awry. This equipment is not designed to withstand water flow in reverse direction; therefore, it must be taken apart to clean. That said, these filters are cleaned in the same manner as a DE filter teardown. Hosing the surface debris off the cartridge is only the first step. Body oils and lotions are the number one contributor to a plugged cartridge filter. Therefore, getting the oils and lotions off the cartridge surface is the difference between frequent media replacement and cartridges that last longer between cleanings.
The oily buildup on the surface plugs up the pores on the cartridge, which restricts water flow and creates a very sticky surface. These filters trap debris on the surface; when the filter is turned off, it falls to the bottom of the tank to free up more surface area for the next cycle. If the surface of the cartridge is sticky, the debris does not fall away, which causes the filter to plug up rather quickly.
Many pool service professionals now offer cartridge filter cleaning services. In addition to hosing off the filter, the media is soaked in muriatic acid along with a cleaning agent. Then, it is re-soaked in a liquid chlorine bath to brighten and lighten the filter (making them look nicer when they are returned to the client). Finally, the filters need to be air dried before they can be used again.
Allowing them to dry completely gives the cartridge fibres time to fluff back up, which is important because they need to expand for the filter to be effective. If they can be pushed down easily, it reduces the filter cycle.
Many service companies suggest to their clients to have two sets of cartridges so they can continue to use their pool while the other set is being cleaned. The most effective system is for the service tech to take the filter media when they close the pool for the season, clean it at their shop, then return the filters ready-to-use in the spring when the pool is re-opened. Since pools are typically at their dirtiest during spring opening, those cartridges are filtering more debris than usual. In fact, some service professionals change the filters after starting up the pool. Once the water is clear, they install new filters to provide a more productive filtration process over the course of the summer. This also extends the lifespan of the new filter cartridges.