Check the flow of water from the retun jets. If the return flow is strong and steady, the filter is fine. If the return flow is weak and sluggish, it’s time to tend to the filter. Filters are equipped with pressure gauges, but these gauges are notoriously innaccurate. As a very general rule of thumb, a rise in pressure of 8 to 10 pounds above normal operating pressure indicates that the filter requires service.

Diatomaceous Earth (DE) filters use a powder called diatomaceous earth to strain out impurities. Diatomaceous Earth is a fine powder, made from the pulverized fossils of aquatic plants. This product is very inexpensive, and readily available at home and garden centers. Each time you backwash a DE filter, you flush both accumulated dirt and debris and spent DE from the filter cannister. FRESH DE MUST BE ADDED AFTER EACH BACKWASHING! Failure to replaenish the cannister with fresh DE can cause severe damage to the internal elements of the filter.

There is a simple formula to figure out how much DE should be added to your filter. First, determine the size of your filter. Filter size is determined by the square feet of filtration area inside the filter cannister. This number is found on a specifications plate on the front of the cannister. (Most filters carry a filtration area of 36, 48, 60, or 72 square feet.) Using a one-pound coffee can, add one can of DE for every 5 square feet of filtration area. It’s OK to round off to the nearest multiple of 5; the filter won’t mind a tiny bit of extra DE, and after all, this is your swimming pool, not the SATs. A 48 square foot filter requires 10 cans of DE. A 36 square foot filter will function effectively on 7 cans.

Even with regular backwashing, DE filters get grimy with time. It’s a good idea to have your filter dismantled and cleaned at least once a year. This affords an opportunity to check internal elements for wear, and to ensure that the filter is working at peak efficiency.

For those of you with cartridge filters, you can improve your filtering efficiency up to 50% by adding 2 coffee cans worth of Diatomaceous Earth to your filter. This is accomplished by adding the DE through the skimmer with the pump on, and stirring it in the skimmer until it is totally dissolved. Each time you hose down the filter cartridges, you’ll have to replenish the DE. Even with DE coating the cartridges, it’s perfectly safe to hose down the filter elements on your lawn. DE is safe for grass and plants, and as a valuable side benefit, it is an extremely effective snail killer!