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Cleaning pool filters
There are several ways to clean filters. The most common method of cleaning is backwashing. The following are detailed best practices and tips to perform this procedure for each type of filter.
Sand filters
First, service techs must determine the proper backwash flowrate (56.7 to 75.7 lpm [15 to 20 gpm] per square foot). For example, a 0.29 m2 (3.1 sf) sand filter needs no less than 176 lpm (46.5 gpm) and no more than 235 lpm (62 gpm). Using too much water flow can potentially lift the sand bed and pass it to waste. In a worst case scenario, the laterals and or filter tank can become damaged from the sand blasting effect as the water is introduced at the bottom of the tank at a high velocity.
If there is not enough water flow, the debris from the sand bed will not be completely removed. As a result, any debris remaining in the filter works its way deeper into the media. When this happens, the dirt in the bottom of the filter can turn to caliche (a hardened natural cement of calcium carbonate that binds other materials such as gravel, sand, clay, and silt). Should this occur, the filter must be replaced; in most cases this buildup cannot be removed because of its size and difficulty to break apart.
Another problem can occur if the sand filter is backwashed too frequently. In some cases, silt can pass through the filter even when it is clean. As a result, service centres will likely receive calls from pool owners explaining they have sand in their pool and additional sand comes out of the pool returns when they vacuum. To begin diagnosing this situation, service techs should ask the client if the ‘sand’ makes a pile or a cloud when they brush their pool. If the former occurs, there could be an issue with the filter. If the latter happens, it is not sand, it is silt. If silt is the problem, it means the sand filter is too clean and, therefore, should not be backwashed. When a sand filter is clean, it allows larger particulate to pass through. This is a sign to stop backwashing the filter and, instead, allow it to load up so it will begin to trap the silt. A clarifier or flocking agent can also be added to help with this process.
Determining how long to backwash a sand filter should not be determined by looking at the water flowing out of the backwash line. Sand filter backwashing should be completed in three minutes. Service techs should use a stopwatch when performing this task rather than guessing.
