A properly sized sand filter should be able to operate continuously for 4 weeks between backwashings. If it is less than 4 weeks, this may indicate sand problems (or sizing problems).

Sand in the pool?

This is never a good sign. If it hasn't made its way into the pool by some other means, it's likely coming from the filter. This could be because of a broken lateral or standpipe. You'll need to empty the tank, locate and make the repair, refill with fresh sand and test.

Sand bed replacement:

To replace filter sand, you'll first need to get rid of the existing sand. One method is to spread a tarp out beneath the filter drain assembly. Then remove the entire assembly and turn on the pump. The water pumping through the filter should remove most of the sand by pushing it out through the drain hole. Another method, which will take much longer is to remove the drain plug only and allow the filter to drain for several hours or days. Then, remove the top dome or multiport valve.

If you have the Triton style dome on the top of the filter, you'll need the special octagonal dome wrench to remove the dome from the filter. Once the dome is removed, gently twist the baffle/pipe out of the way so you have enough room to scoop out the sand.

If you have a Top Mount Multiport, you may need to cut some pipes to remove the valve, however, you can reconnect them later with unions or couplings. Once these pipes are cut, remove the clamp band connecting the valve to the filter. The valve should then pull straight up and off. Plug, tape, or cover the standpipe so you don't accidentally spill sand in it. Then you can use a shop vacuum to suck out the sand, or a small cup to scoop out the sand.

Be very careful as you scoop or suck, not to hit or break the laterals at the bottom of the tank. They can be brittle when they get older, and it’s probably a good idea to replace laterals at the time you replace the filter sand. Use a hose to wash out the sand beneath the laterals. When the tank is empty of sand, replace the drain assembly, using silicone sealant on the threads. Then add enough water to cover the laterals, this is so the new sand pouring in won't crack them.

Pour the sand in. Use only specially graded pool filter sand; #20 silica sand, 45 - 55 mm. If you have a top mounted multiport filters, use care to keep the lateral/ hub assembly centered, and on the bottom of the tank. After each bag of sand is added, make sure it is still centered. It may be useful to have a helper hold the standpipe steady while the sand is added.

Add the recommended amount of sand only; do not add more than necessary. This can lead to problems. If you don't know the right amount, contact your dealer or manufacturer. Most tanks are filled only about 2/3 of the way full, to leave enough free space on top. When full, lubricate the o-rings and reassemble filter top. Make sure lid is very secure, otherwise the lid could blow of and create a hazardous situation. It's a good idea to replace the o-ring on the filter domes.

When the filter is started up, begin on "RINSE" setting first (if you have a multiport valve). Then backwash and rinse again. If you have a push-pull valve, backwash first. This will prevent putting a lot of "sand dust" into the pool after a sand change.

Leaking filter?

Sand filter tanks rarely leak themselves, however leaks often occur in and around the multiport interface. One of the most common complaints is that water is leaking out of the backwash port of the multiport valve. Slight adjustments of the handle may solve this problem, but only temporarily. A more permanent repair may require replacement of the spider gasket inside of the multiport. You may also have leakage up around the middle of the handle on the valve. This usually requires replacement of a Teflon washer and sometimes the spring as well.

You may have a push-pull valve, or slide valve, instead of a multiport valve. Leaks can occur through the top of the index plate, or out of the backwash line. This may help to determine what o-rings need to be replaced. Leaks can also occur at the bulkhead unions where the valve attaches to the side of the filter, or around the threads on a top-mounted multiport. The drain plug can leak if not tightly secured or properly sealed.

Filter replacement?
A filter will last you for a long time, but not forever. A new filter may be in order if your current filter is between 15 and 20 years old, or difficult to use or get parts for. If the filter tank has cracked, usually from freeze damage or possibly from closing off return valves while the pump is running, a new filter is in order. Replacement is usually fairly simple, with just a few plumbing fittings needed.