After a number of years the sand in your pool filter will no longer be able to filter the water effectively. From a manufacturer standpoint it is recommended that you change the sand in your filter every 3-4 years. This will maximize the effectiveness of the filter and help you to maintain clean and clear water.
Removing the sand with a shop vacuum will be much easier than scooping the sand out by hand or with a small shovel. The sand in an old filter can actually be laden with bacteria so it would be better if you minimize your direct contact with the sand.
After removing the old sand you will want to add water to the tank before adding new filter sand. This water helps to absorb any impact of the falling sand on the lateral assembly.
The type of sand that you add to the filter will be silica sand which is specifically produced for filter media. This sand is between 40-50mm in diameter and is available from most swimming pool supply stores. Do not substitute other types of sand or you will almost certainly have problems with your filter and potentially damage the pool.
The amount of sand that you add to the filter will depend on the size of filter that you have. You must be certain to find accurate information about how much sand to use in your filter. Over filling or underselling the filter will at least cause the filter to not function properly, and at worst cause damage to the filter. Filter sand sizes range typically from 100 or 150 lbs all the way up to 600lbs or more for large pools. Sand typically comes in 50lbs bags. If you filter is a 300 lb filter simply divide by 50. In this case you would use 6 bags.
Be sure not to get any sand into the sandpipe. Cover the top of the pipe with duct tape. It is also very important that the sandpipe is directly in the center of the filter as once you have filled with sand you will not be able to adjust the position of the sandpipe. If not centered you will not be able to get the valve head back on the filter and will need to start all over again.
Once full you can put the filter head back on being absolutely certain that it is tight enough. This is where a skilled hand is helpful. If you over tighten the filter head then you may actually crack the filter body which would require replacement of the entire filter tank.
Once reassembled the first thing you need to do is give the filter a thorough backwash. You should start this process by over filling the pool and then backwashing for as much as 3 to 5 minutes, followed by a 60 second rinse cycle before setting to “filter”.