A sand filter remains one of the popular options for owners to utilize to clean the water from their salt water swimming pools. While you can also consider cartridge and D.E. filters, sand filters tend to be the least expensive option to purchase and the easiest to install.
Sand filters typically hold between 50 lbs – 700 lbs of sand depending on the tank size and capacity. Follow the instructions for your specific sand filter model and don’t exceed the capacity but also leave around 6″ of space at the top of the sand filter. So if you’re filling your sand filter with a bag of sand that is already opened and don’t know the exact weight, use the 6″ empty space at the top of your filter as the guide. The larger the volume of water in your pool, the bigger the sand filter you will require.
Sand filters use a special type of sand that is poured directly into the filter unit. Water enters the filter and the sand helps to pull out contaminants and debris so that the water that leaves the tank is clean and is then returned to the pool. Sand filters need to be backwashed regularly which involves opening a water valve and flushing water from the pool through the filter through a hose that drains somewhere until the water is clear. This typically takes several minutes so it can involve removing significant amounts of water.
Sand for use in a sand pool filter typically costs about $25 – $50 for a 50 lbs bag. Sand needs to be replaced every 5-7 years and generally costs $100 – $200 to refill a sand filter depending on filter size. Unless you have a large pool with a 700 lbs sand filter which may cost closer to $350 – $700 at the high end.
Sand Loss During Backwashing
Sand from a sand filter should not be lost during backwashes. So you should not have to add more sand to your filter over time with backwashing. Instead as mentioned above, sand should be completely replaced at one time typically every 5 – 7 years depending on your pool usage and how dirty your pool gets.
If you notice sand loss during backwashing or notice that sand is entering the pool water, it’s likely you are suffering from one or more of these problems.
Too Much Sand
As mentioned above, follow the maximum weight limit of your filter when filling it with sand but also leave 6″ of head space at the top of the filter with no sand. Filling the filter with too much sand can cause it to leak out when backwashing or cause it to enter the pool and reduces filter and backwashing capabilities.
The Sand Is Too Fine
Often when replacing sand, fine sand may be part of the sand that you’re adding to the filter. It may be too fine for the filter. When changing sand, do a backwash to pack the new sand and rinse out sand that is too fine for the system. Also ensure you use the recommended sand as suggested by the filter manufacturer.
You need to use sand that is specific for sand filter pool usage and not play sand or sand that you’d buy from a garden center. As mentioned above the fineness of sand matters and other sands are too fine to be used successfully in a pool sand filter. Use the sand recommended by your filter manufacturer or short of that, your pool company.
If your filter has broken laterals, a damaged valve gasket or is a cheap system to begin with, you may notice sand loss. A filter may have parts to be replaced or otherwise repaired.
Sand Filter Settings
Filter: Used for normal pool filtration and when vacuuming the pool. This is the setting you will use at most times.
Backwash: Used to clean the filter sand when the filter pressure gauge reaches a point that indicates that the filter is full of debris.
Rinse: Used to clean water inside the filter tank.
Waste: Used for vacuuming heavy concentrations of dirt directly.
Closed: Shuts off the flow to the filter and pool.
Typically backwashing of your pool sand filter should occur once per week. With frequent pool usage or with pools that get dirtier than “normal” you may have to backwash twice per week. The best time to backwash is right after vacuuming your pool.
As with washing a cartridge filter for people who have that sort of filtration system, the best time to backwash a sand filter is right after cleaning a dirty pool. The pool has been cleaned of contaminants which are now sitting in the filter. Backwashing the filter removes these contaminants from the pool system completely so they can’t escape from the filter and return to the pool water.
Rule of thumb: Get to know your sand filter pressure gauge. When it reads 8 to 10 psi (pounds per square inch) above the normal starting pressure, this is an indication that the filter has reached its debris-holding capacity and needs to be cleaned. Backwashing too frequently simply increases your work, the water your pool uses and wastes, and thus your water charges.
Speaking of which…
Water Loss From Backwashing
One backwash might remove 200 – 300 gallons of water from your pool depending on how long you allow the backwash to last and how powerful your pump is. The more water you remove from the pool, the more water you clearly will have to add back to the pool to replace it. This increases the cost of water but also impacts your water chemistry.
The more water you remove from the pool through backwashing the more it can change your water chemistry. When you drain water in large amounts, it can pull certain aspects of your pool water out of whack which may add more work for you in the form of adding chemicals or adjusting your pool system to fix the water balance.
Each sand filter is rated with a maximum sand capacity that is specified by the manufacturer. This should be used as the guideline for filling a sand filter with sand an refilling it again as required most likely in 5-7 year. Backwashing is a necessary maintenance task for sand filters that generally occurs about once per week or when the filter’s gauge is about 8 – 1- psi higher than normal.
Sand should not be lost during backwashing so you shouldn’t have to refill a sand filter for lost sand. If you are losing sand you most likely have one of the issues as mentioned above that need to be addressed.