Diatomaceous Earth (Also called D.E.)
A powder made of the desiccated shells of diatoms, used as a filtering agent.

Diatomaceous Earth Filter (D. E. Filter)
A filter designed to use diatomaceous earth as the filter medium. The D.E. is added through the skimmer with the pump on, which deposits the D.E. on a grid.

Dichlor (Sodium Dichloro Isocyanuric Acid)
A quick dissolving chlorine compound made up of chlorine and cyanuric acid (stabilizer) and has a pH of 6.9.

EPA
Abbreviation for the U.S. Environmental Protection Agency.

Efficacy
The power to produce an effect. Chlorine's efficacy is affected by many factors, including the sun, temperature, water balance and the water's chlorine demand.

Enzymes
Used in commercial swimming pool formulations to break down and destroy oils in the swimming pool.

Equalizer Pillows (Also Air Pillows)
A vinyl pillow used in winter months to absorb freezing water’s pressure and helps to protect the pool walls. The Air Pillow also reduces the amount of excess rain, snow, and leaves on the winter pool cover.

Filter
A device that removes un-dissolved or suspended particles from water by the flow of the water through a porous substance (a filter medium or element). The three main types of filters used in pools are sand filters, cartridge filters and D.E. (diatomaceous earth) filters.

Filter Aid
A chemical compound added to the water, filter or skimmer that allows the existing filter to become more efficient. They are generally flocculants, coagulants and diatomaceous earth.

Filter Elements
Devices inside the filter designed to trap suspended solids as water flows through it from the pool. These should be chemically cleaned twice a year.

Filter Medium
The material used in the filter to trap suspended dirt particles as the water flows through it. It is the polyester or paper in a cartridge filter element, the sand in a sand filter and the diatomaceous earth in a D.E. filter.

Filter Powder
A common name for diatomaceous earth (D.E.), the filter medium in a diatomaceous earth filter.

Filter Sand
Sand made up of hard and sharp silica or quartz (or similar), which have been graded for size and uniformity, and is used as the filter medium in sand filters.

Flocculants
Virtually the same as a coagulant, it is a chemical substance (such as alum) that is used to clump suspended particles or algae into a heavy mass, which can be caught by the filter or sinks to the bottom of the pool for vacuuming.

Foam
A froth of bubbles on the surface of the water. Usually comes from overuse of algaecide but may also be caused by soaps, oils or other contaminants carried into the water by swimmers.

Free Chlorine (Available Chlorine)
Chlorine in a form capable of destroying bacteria and algae. Preferred range: 1.0 to 3.0 ppm.