Sand filter is a filtration system employing a bed of silica sand to filter out contaminants of foreign material that is not wanted in swimming water. When new this sand is very rough with a lot of jagged edges. As the sand ages the edges get rounded off and are unable to capture foreign materials. This allows for the sand to get compacted not allowing water to flow through properly. When the sand get compacted it allows for "channels" to be born where water passes through without going through the sand which means no filtering.
When the sand looses its "edge" it can not properly remove UDS (undissolved solids) from the water or small materials. This means you have to increase chemical usage substantially to compensate and this will have negative side effects. Best solution is to change the sand.
As sand gets older and compacted water is unable to flow through properly. This means that suction based cleaners do not have enough water flow to operate and return based (in floor pop-ups and most Polaris* cleaners) are lacking the needed pressure to operate. If this is the case, changing the sand or filter is the only option.
When this happens it is always due to broken laterals. When a lateral gets broken you need a sand change to get to the laterals to replace them. Replacing laterals is not included with standard sand change.
There are two things different approaches depending on the back wash valve location. If the back wash valve is on top of the filter the technician will have to cut pipes and re plumb the connection when done (extra cost) other wise...
No, play sand is too smooth and will not properly filter foreign materials from the water.
* Polaris is a registered trademark of Zodiac Pool Systems, Inc