Make Filter Media Last

By Trevor Sherwood

Like any other pool component, filter media must be maintained to ensure a long and productive life. But what exactly does that mean? Are pool operators doing what is expected to stretch every dollar to capacity? Take a look at the recommendations below for backwashing and cleaning a cartridge filter properly.


How often should a filter be backwashed?
Backwashing is defined as the process of cleaning a swimming-pool filter by reversing the flow of water through the filter. Only sand filters and diatomaceous earth (DE) filters can be backwashed.

Many use this process as a “cure-all” technique for problems ranging from cloudy water to unbalanced chemicals. Backwashing, too often and when not necessary, is essentially like creating a leak. When the pool has a leak, it loses more than just water.

During backwashing, fresh water must be added to a pool to cover what was removed during the process. As a result, the fresh water dilutes the current water chemistry, which amounts to additional expenses for more chemicals and water, as well as sewer in many areas.

Pools with heaters also incur costs to return the temperature of the water up after adding fresh water; the heater must operate more to maintain the temperature, which increases utility costs, such as gas and/or electric.

The amount of labor also increases when the 3 to 5 minutes a day spent backwashing is considered.

Ultimately, backwashing should not be done according to a predetermined schedule; rather it should be based on pressure differentials.

Why and when should a filter be backwashed?
For sand filters, manufacturers recommend backwashing only when the filter pressure reaches 8 to 10 pounds per square inch (psi) above the previous time the filter was backwashed.

On filters with both influent and effluent gauges, the differential should be 10 to 20 psi between the gauges. As the filter becomes dirty, the dirt clogs the pores in the sand and helps the filter to hold even smaller particles. Therefore, as the filter media become “dirtier,” they are able to filter down to a smaller micron and work more efficiently.

For DE filters, backwashing is recommended when the pressure reaches 10 psi over normal operating pressure. With DE filters in some areas, a separation tank is required to collect the backwashed water, which includes DE. When a DE filter is backwashed, fresh DE needs to be added after the process to recoat the screens.

For any filter, backwashing should be performed for 3 to 5 minutes or until the sight-glass clears.

When a pool or spa has cloudy water, it is often due to one of two causes--water balance or filtration. Upon testing the water chemistry--if the readings are within acceptable ranges per the state bathing code--it is time to inspect the filter and recirculation equipment.

The first check is the flow rate per the flow meter.

Those keeping accurate logs should be able to tell if there is a problem with flow. The flow rate is calculated by taking the volume of the pool divided by the state’s turnover rate divided by 60. If the flow rate is not greater than or equal to this number, ascertain why it is not meeting the flow.

Some of the easiest actions to take are to empty the pump basket, clean the skimmer baskets, and make sure all valves are in the correct position. If the flow rate still does not improve, it is now time to backwash.

What about cartridge filters?
Cartridge filters do not provide the option to backwash; rather, they need to be cleaned manually, which is a lengthy process. It involves shutting down the filtration system (pump included), manually removing the cartridges, and cleaning with a high-pressure hose to remove oils, grease, dirt, and scale.

After cleaning, if there are still oils, grease, dirt, and scale, use the following process:

Note: Always turn off the pump before doing anything to a filtration system. Also, be sure to follow the manufacturer’s directions.

1. Open the filter-drain valve and air-relief valve (if applicable).

2. Take off the lid to remove the cartridges.

3. Spray each cartridge with a hose.

4. Soak the cartridges in a Tri Sodium Phosphate (TSP) and water bath overnight.

5. In the morning, spray each cartridge with a hose.

6. Soak the cartridges in a muriatic acid and water bath (ratio of 1 to 15) overnight.

7. The following morning, spray each cartridge with a hose once again.

The cleaned cartridges are now ready to be reinstalled. First, replace the lid. Remember to close the filter-drain valve and air-relief valve. Start the filtration system (turning on the pump) to see if all parts are assembled correctly.

If the filters leak, turn off the pump and make sure the gasket has a tight seal before turning it on again.

It is highly recommended to have a spare set of cartridges on hand so the pool or spa will not be shut down from the two-day cleaning process. If this is the case, be sure to allow the cleaned cartridges time to dry then store them for later use.

How long will filter media last?
With continual use and backwashing or cleaning, filter media do have a life expectancy. The sand in sand filters may last between 5 and 15 years, as long as the top layer of sand is changed annually.

The DE in a DE filter generally lasts 4 to 6 months, and the same between cartridge cleanings.

High bather loads diminish the life expectancy of filter media. Again the more the filters are backwashed/cleaned, as well as the higher bather load, the less life expectancy the filter media will have.

As with everything, be sure to follow the manufacturer’s directions when backwashing/cleaning or replacing filter media. Do not use backwashing as a part of the routine, but rather when needed to get the most out of a filtration system.

Trevor A. Sherwood II is the owner of Pool Operation Management, a pool-consulting company, in Brick, N.J. Reach him at (732) 451-1040.