The outside of this type of filter is usually made out of fiberglass or stainless steel, and it is partially filled with silica sand. As water circulates from the pool through the filter, water enters at the top and percolates downward, leaving most of the oils, debris, and other impurities trapped in the sand, thus allowing clean water to return to the pool.
The filter is usually backwashed once per week, a process which reverses the flow of water through the filter. This lifts most of the contaminants from the sand and washes them out the backwash line, along with a volume of water. Eventually the filter becomes overburdened from minerals in the water and from the volume of debris (dirt, dead algae and bacteria, etc.) remaining in the sand, causing the sand to be hard and compacted. This reduces water flow throughout the system, and can cause cloudy water, poor heater operation, and increased wear and tear on the pump. Approximately every 3 to 5 years the old sand will need to be removed, and new sand added. If the pool is painted, the sand may need to be changed annually.
The efficiency of the sand filter, as measured by the largest-sized particle that can pass through it without being caught, is 40-50 microns. (A micron is a millionth of a meter.) In the past, more sand filters have been installed in some areas because of the supposed “ease of use” for the pool owner, but drawbacks of the sand filter include:
- Longer hours of operation are required to properly filter the pool water
- Filtration efficiency (compared to other types of filters) is inferior, especially in hot climates
- Higher chlorine levels are usually required on pools with sand filters to help reduce the risk of the pool water turning green
- Because of frequent high-flow backwashing, this type of filter wastes more water
- Since homeowners rarely see the inside of the filter, and since the sand usually lasts for years, maintenance on sand filters is frequently neglected
Cartridge filters come in various sizes and shapes. Most of the filter canisters (or tanks) are stainless steel, but some are made of a hard plastic or fiberglass. There may be as few as one or as many as fifteen or more cartridge elements inside a cartridge filter. The cartridge elements are cylindrical, and made of a paper-like fiber. As the water passes through the elements, impurities are collected on the element material. Cartridges remove smaller debris from the water than sand; its micron rating is about 20 microns. This filter is cleaned about once a week by removing the elements from the canister and hosing it off using a high pressure nozzle.
Drawbacks for the cartridge filter include:
- Most cartridge filters are for smaller pools and spas containing approximately 12,000 gallons of water or less
- There is no mechanical method for backwashing these filters – it must be done by manually disassembling the filter and hosing it off weekly
- The cartridge elements need to be replaced as they become old and worn: about every 2 years, which can be expensive, depending on the size, style and brand of cartridge
- Pools with cartridge filters tend to develop high dissolved solids levels (TDS) faster than sand or D.E. filters, because there is no water removal via backwashing.
D.E. (Diatomaceons Earth) Filters:
The majority of D.E. tilters are made of stainless steel, with a few being made of fiberglass. The elements inside consist of a series of plastic grids covered with a cheesecloth-like fabric. A white powder, known as D.E., is added through the skimmer and mixes with the water as it heads toward the filter. As the water passes through the filter, the D.E. powder coats the outside of the elements. This coating traps microscopic impurities which cannot be trapped by sand or cartridge filters, and therefore provides better water clarity in the pool. The efficiency rating of a D.E. filter is about 3 microns. This means you can filter anywhere from 15% to 50% less per day, which results in reduced electric bills, and extended motor life.
Especially in drought areas, D.E. filters are most commonly recommended and installed because of the lower water requirements for cleaning (compared to the sand filter).
Drawbacks for the D.E. Filter:
- To clean this type offilter, the filter must be taken apart in order to hose the elements off with water.
- Each time you backwash, or clean the grids, you need to re-charge the filter by adding two to four pounds of D.E. powder (which is very inexpensive) through the skimmer. However, since modern D.E. filters can go as long as 6 months to a year between cleanings, this is not much of a drawback! Older D.E. filters usually are cleaned quarterly