Sand Pool Filters

Sand Pool Filters

Sand Pool Filters

The sand in a pool sand filter (#20 silica sand; 45 - 55 mm) is specially graded to trap particles in the 20 - 100 micron range. As a sand filter collects dirt, its efficiency increases, trapping more dirt. When your pressure gauge shows a reading 8 - 10 lbs. over the clean, start-up reading, it is time to backwash the captured dirt out of the filter.

Pool sand filters are known to be the lowest maintenance of the three types of pool filters. You may only need to open up the tank every 5 years or so. DE filters require removing the internal grid assembly at least annually to clean them well, and cartridge filters don't backwash, you remove the cartridge and hose clean every so often, depending on the cartridge filter size. Sand filters are the easiest to operate and maintain.

"They say" that the sand inside a sand filter should be replaced after seven years. Gradual loss of efficiency may be hard to notice. A sand filter requiring more frequent backwashing than in the past is one sign of sand deterioration. Another is the overall quality of the pool water, or if you need to run your pump more, or use more chemicals, to maintain water quality.

Pool Filter Sand Problems

Pool filter sand often becomes "mudballed" containing small clumps of oily gunk, or it may become "channeled", which is when water has worked open holes in the sand and is streaming right through (without really going through the sand). In hard water areas, it can "calcify" with calcium deposits, literally turning the filter sand to sandstone. Other water balance problems or an oversized pool pump can also contribute to pool filter sand deterioration, but a properly sized sand filter without such problems could go over 10 years between sand changes.

Use of Biguanide chemicals, such as Aqua Silk, Soft Swim or Baquacil requires an annual cleaning of the pool filter sand with sand filter cleaner to prevent it from "gumming-up". High amounts of bather oils can also gum-up a sand bed. Enzyme pool treatments can help control oil problems in pools.

Many years of forced water wears away the sharp edges of pool filter sand. Over time, the sand grains become more circular, losing their sharp edges, and their ability to trap small particles.

Adding a small amount (1 cup) of alumn, or cellulose fiber like Filter Fiber, through the skimmer will form a gelatinous layer on top of the sand bed, useful in cleaning up an undesirable water condition. You can also add a small amount of D.E. powder. Clarifiers are also helpful for sand filters that don’t seem to catch everything, which is common. Clarifiers coagulate smaller particles together for easier filtration. The Slime Bag is a mesh fabric bag that attaches to your return fitting as a secondary filter. For a more permanent boost, replace your regular pool filter sand with Filter Balls or ZeoSand, two pool filter sand substitutes, or alternative pool filter sands.

How and When to Backwash a Sand Filter

When the pressure gauge on your sand filter is reading 8 - 10 lbs above the clean, starting pressure (after backwashing), it is time to backwash your sand filter, again. This process involves turning a valve so that the water will flow through the filter backwards, flushing out the dirt - Hence the name "back-washing."

Pool water normally flows top to bottom in a sand filter, water enters at the top of the tank and pushes down through the sand bed into the laterals at the bottom of the tank. During backwashing, the water flows in reverse, from bottom to top, out of the laterals and up thru the sand, to flush out the trapped dirt from the sand bed, and send it out the waste line.

Sand filters can have either a push-pull valve (also known as a slide valve) or a multiport valve. The multiport valve has multiple ports on the valve, usually 6 positions, hence the name “multi-port”. Slide valves have only two positions, filter or backwash, with a plunger being pulled up or pushed down to change positions.

Always shut off the filter pump before turning the filter valve, or it could damage the gasket or internal filter parts. It can create a brief dead-head or water hammer effect, which could rupture filter tanks, pipe fittings or valves, and possibly injure those nearby.

1. FILTER: Keep it here all the time, except when backwashing, rinsing or wasting
2. RINSE: Use this setting for 15 seconds after backwashing to rinse the sand filter tank
3. RECIRCULATE: A filter bypass setting. Use this if your filter's broken or leaking; at least you're circulating the water
4. BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open and your backwash hose is rolled out
5. CLOSED: Put here to close off flow from the pool, usually to work on the equipment, or prevent backflow of water out of the filter. Do not operate pump with valve in the closed position, and don’t use it as a winterizing setting, pop-up the handle midway between two positions for winter.
6. WASTE/DRAIN: Another filter bypass setting, but this setting sends the water out of the waste pipe (hose), instead of returning it to the pool. This setting is used to lower pool water level or to vacuum to waste, which is best when vacuuming algae or heavy amounts of dusty, silty debris.

To backwash a sand filter with a multiport valve:

-- Shut off the pump motor
-- Press down on valve handle, rotate valve from FILTER to BACKWASH position
-- Roll out any backwash hose or open any valves on the waste line
-- Open air bleeder assembly on top of sand filter, and turn pump on.
-- Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly if the pressure gauge spikes or if the hose kinks up.
-- Let the pump run for 2 - 3 minutes on BACKWASH or until waste water turns clear
-- Shut off pump motor and move multiport valve handle to RINSE position. Turn pump back on and rinse for 15 seconds. This resets the sand bed, and flushes out residual dirt out the waste line.
-- Shut off pump motor (again) and move multiport valve handle to FILTER position
-- Turn pump back on and note the lower pressure. Mark it on the filter tank!*

To Backwash a sand filter with a slide valve (push-pull valve:

-- Shut off pump motor, roll out backwash hose (if you have it)
-- Twist to unlock plunger T-handle, pull / twist plunger upwards 2 - 3" (Pentair valves are reverse)
-- Open air bleeder assembly on filter, and turn pump on
-- Watch pressure gauge for backpressure (over 30 PSI) and hose for kinks. Be prepared to shut off pump quickly if pressure gauge spikes
-- After hose fills with water, backwash your sand filter for 2 - 3 minutes or until water runs clear
-- Shut off pump motor and push T-handle back down into locked position
-- Turn pump back on and note lower pressure. Mark it on the filter tank!*

  • I like to use a permanent marker and write the clean/dirty digits right on the filter tank, for example, 8/16 to serve as a reminder when to backwash that particular sand filter. All pool filter systems have different operating pressures, and your filter system will also have its own specific pressure range, from clean to dirty.

A properly sized sand filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashing. A "Filter Run" of less than 4 weeks may indicate sand problems (or sizing problems), or unusual water conditions being cleaned up.

Most manufacturers suggest that a filter pressure of 8-10 psi greater than the clean, start-up pressure is when you should backwash. However, if your flow seems to diminish considerably at only 5 psi higher, or if pressure rises very rapidly, you may have a sand pool filter that’s a bit undersized, overworked or in need of a sand change.

As mentioned before, sand pool filters operate a bit more effectively when they are half dirty than when they are fully clean. Backwashing a sand filter too often could lead to cloudy water. Assuming that your pressure gauge is functioning properly, resist the urge to backwash a sand filter until it’s climbed at least 5 psi higher than the clean pressure.

Filter Sand in the Pool?

Bad news. If sand has not blown in, or been carried in on the feet of swimmers, its likely coming from the filter. A broken lateral or standpipe may be the cause. You'll need to empty the tank, locate and make the repair, refill with pool filter sand and test.

If you have overfilled your sand filter during a recent sand change, it is not uncommon to experience a small amount of "blow back" into the pool after backwashing. You may also see some sand discharged from the backwash hose after backwashing. Both normal, but continued sand leakage during filtration usually indicates a lateral breakage. Don't confuse dust with pool filter sand. Dust and silt will ‘dust-up’ off the pool floor when you touch it with a pool brush, while filter sand grains will roll around on the floor and not dust up very much.

It is common to experience a small amount of dust returning into the pool after backwashing a sand filter, even when using the Rinse setting afterwards. If you have a problem with fine dust constantly passing through your sand filter, you can vacuum this out to waste after filling the pool first. If this problem continues, you may have sand bed problems, or a sand filter that is too small for the pump. The Slime Bag is a product specifically made for the problem, and is quite effective.

In areas of high dust or pollution, clarifiers can help by increasing the particle size by coagulating smaller dust into more easily filtered clumps. Sand filter cleaners or enzymes are helpful products to remove trapped oils and gunk, which gets trapped, mostly in the top 2 inches of the sand bed. In fact, replacing just the top 25% of your filter sand with fresh pool filter sand, is a quick way to rejuvenate an overworked sand pool filter, and extend the time between complete sand replacements.

Filter Sand Replacement

Filter sand lasts 5-7 years on average, but for very small filters, or for systems with too much water volume, or using Biguanide sanitizers, 1-2 years may be all you get. A good first way to extend filter sand life is to use a Sand Filter Cleaner once or twice per year, to remove minerals and oils that can clog a sand filter, or make filtering inefficient.

When replacing pool filter sand, use only products labeled as Pool Filter Sand, or Pool Filter Sand Alternatives. Sand for pool filters is graded, to .45-.55mm size, otherwise known as #20 silica sand. Pool filter sand can be purchased at larger home stores, or a gravel / sand yard, or water treatment stores, local pool suppliers, or online.

To replace your filter sand, you'll first need to empty out the existing sand in the tank. Start by removing the drain plug and allow the filter to start draining water. Then, remove the top dome or multiport valve from the top of the filter.

If you have the Triton style dome on the top of the filter, with a side mounted filter valve, you'll need the octagonal dome wrench to remove the dome. If you don't have a dome wrench, you can use a large strap wrench or in a pinch, a large flathead screwdriver and hammer. Once the dome is removed, gently push the baffle/pipe out of the way (left or right) so you can get a scoop to the sand.

If you have a Top Mount Multiport, you may need to cut some pipes to remove the valve. Leave some clear pipes, so you can reconnect them later with pvc unions or couplings and some pvc glue. Once these pipes are cut, the clamp band connecting the valve to the filter tank is removed, or in the case of older sand filters, several bolts are removed. In either case, a top mounted multiport valve pulls straight up and off. You may need to use a little effort with some prying and twisting to release the valve off of the standpipe and flange. When you get the valve removed, stuff a rag or plug into the standpipe so you don't spill sand in it. Then you can use a shop vacuum to suck out the sand, or you can use a large plastic tumbler cup to scoop out the sand.

Be very careful as you scoop or suck the sand out, not to knock or break the laterals at the bottom of the tank. They can be brittle when they get older, and it may be wise to replace the sand filter laterals at the time you replace the filter sand. Once all of the sand is scooped out, you can gently tip the tank over and use a hose to wash out the sand beneath the laterals. If you can easily remove the entire drain assembly at the bottom of the tank (Pac-Fab sand filters, and others), you can rinse it out through the drain hole, but getting every last grain of sand out is not really necessary. If you do remove the drain assembly entirely, use Silicone sealant and Teflon tape on clean threads to re-tighten the drain assembly fully, to prevent leaking.

When the tank is empty of sand, replace the filter tank in the proper location and then add enough water to cover the laterals, so the new sand pouring in won't crack them. Again, if you have the top mounted multiport, cover the standpipe opening to keep sand out. If you have a side mounted filter valve, gently push the intake baffle to one side, or wrap the baffle with a small plastic bag to keep the sand from entering the pipe as you pour it in.

Pour the new filter sand in! Use only specially graded pool filter sand. On top mounted multiport filters, use care to keep the standpipe assembly positioned in the center, 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 in place while you pour the sand into the tank.

The best method to add sand to a filter tank, is to set the sand bag onto the tank, and use a razor knife to cut from the bottom‘underbelly’ of the bag. Wear a mask, or keep care not to breathe in the silica dust while pouring, and on older fiberglass sand filter tanks, wear long sleeves to keep from getting "fiber-rash".

Add the recommended amount of sand only; more is not better! If you don't know this info, look it up online, we have this information on most of the sand filters we sell. Most tanks are filled only about 2/3 of the way full, to leave enough "freeboard" space on top. When the tank is full of sand, clean and lube the o-ring and reassemble filter top or valve, using a brush to remove small sand grains that may prevent a good seal. Make sure filter lid is very secure; lids that blow off can be very dangerous. It's a good idea to replace the o-ring on the filter domes, if it is distended or dry-rotted.

When the filter is started up, start up 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 final step will prevent putting a lot of "sand dust" into the pool after a sand change. Afterwards, note your clean, or start-up filter pressure on the gauge, it may be different than before you changed the filter sand.

Leaking Sand Filter?

Sand filter tanks rarely leak themselves, however leaks often occur in and around the valve connection. A common complaint is that water is leaking out of the backwash port of the multiport (six position) valve. If your sand filter tank is leaking, or has small cracks in it, replace it immediately. There is no safe, effective means to patch a sand filter tank. But you can repair leaks around the dome or top mounted valve, or around the bulkheads, on side mounted filter tanks.

Sand filters can also leak from the drain assembly. Try to determine if the leak is from the assembly that is screwed into the body of the tank, or if it is the cap or plug that is leaking. Some sand filter drain plugs have small o-rings or gaskets that need periodic replacement.

You may have a push-pull valve, or slide valve as it is sometimes called, instead of a multiport valve. Leaks can occur through the top of the index plate, or out of the backwash line. Take an easy inspection of the o-rings that may need to be replaced on the plunger.

Leaks can also occur at the bulkhead unions where the valve attaches to the side of the filter. The bulkhead assembly itself may be cracked or loose, or the gasket may have failed. This repair is usually more complicated, as you may need to access the bulkhead from both sides of the filter tank, by removing most of the filter sand.

Leaking Multiport Valve Repair

Is water leaking out of the backwash port of the multiport valve? Slight adjustments of the valve handle may temporarily solve this problem. A more permanent repair may necessitate replacement of the spider gasket inside of the multiport. You may be tempted to install a valve on the waste line, and say to yourself, “There, I fixed it!”, however the valve could also be allowing water to recirculate around the filter, bypassing to the pool. And one of these times, someone will forget to open that valve when backwashing.

You can also have leakage up around the middle of the handle on a multiport valve, which external adjustments rarely fix. This usually requires replacement of the Teflon washers under the handle and the o-rings on the rotor, as it passes through the lid. A floppy handle with no tension usually needs a replacement spring. Valve Rebuild Kits contain all the o-rings, gaskets and washers in one pack. In either case, an easier repair is to replace the “key assembly”, which is the handle, lid and rotor, everything already assembled. Plug and play.

Sand Pool Filter Replacement

Well, they don't last forever, but almost. A new sand pool filter may be in order if your current filter is outdated and difficult to use or hard to locate replacement filter parts. If the filter tank has cracked, usually from freeze damage or from closing off return valves or waste valves while the pump is running, a new filter is in order. It is usually cheaper to replace the entire filter than to buy just the tank, don’t ask me why, but it is.

Replacement of a sand pool filter is usually fairly simple, with just a few plumbing fittings and pipe and the required amount of pool filter sand.

Position the new tank in the correct, final location, making sure it is on level concrete or block slab, or sturdy AC pad. Turn the tank so the label is visible and the drain plug accessible.

Add water to the tank, to fill it about ¼ of the way full. Then you can add the filter sand or filter sand substitute, to the tank. For top mounted valves, be sure to hold the standpipe vertical and centered, flush on the bottom of the tank, as the sand is added. Also, cover the standpipe with duct tape, or a turned over cup, plug or cap, so you don’t pour any sand inside the standpipe.

Add the recommended amount of sand only; more is not better! If you don't know this info, look it up online, we have this information on most of the sand filters we sell. Most tanks are filled only about 2/3 of the way full, to leave enough "freeboard" space on top. When the tank is full of sand, clean and lube the o-ring and reassemble filter top or valve, using a brush to remove small sand grains that may prevent a good seal. Make sure filter lid is very secure; lids that blow off can be very dangerous. It's a good idea to replace the o-ring on the filter domes, if it is distended or dry-rotted.

Installing the Top Mounted Multiport Valve

With top mounted multiport valves, you may be able to use the same threaded pipe fittings from the old filter, just unscrew them out of the old valve. Remove any old sealant, and wrap the fitting 9 times with Teflon tape, to cover all threads with 3 layers. Wrap it only in a clockwise direction around the threads, so it won’t unravel when you tighten the fitting in.

Before you thread in your fittings, check the valve ports for the words PUMP and RETURN. Don’t get the connections switched around! Thread your pipe fittings into the valve, hand tight, plus no more than 1-1/2 turns with a wrench. Overtighten into the valve and it can crack around the port. Make final connections to the plumbing connections, install the backwash hose adapter and pressure gauge with Teflon tape, and you are ready to test the new filter!

When the filter is started up, start up 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 final step will prevent putting "sand dust" from getting into the pool after a sand change.

How to Select a Sand Pool Filter Replacement

Remember that for sparkling water, we need the trio of sanitation, filtration and circulation. If one of these areas is lacking, the water won't look so hot. If you have water troubles, yet you've kept very good chemical maintenance and water circulation is good (and the pump is running for enough time each day), you may have a filter problem.

Is the filter sized properly? Many sand pool filters are grossly undersized, installed by a pool owner or builder looking for the cheapest filter that could be installed. Such marginal sand filters end up costing more money in the long run.

Sand filters are sold in different tank diameters, from 16” diameter, up to 36” diameter, holding less than 100 lbs of pool filter sand, up to 600 lbs of sand. Below are some guidelines for sizing sand pool filters properly.

-- 10,000 - 20,000 gals – 21”- 24” tank
-- 20,000 - 30,000 gals – 24”- 30” tank
-- 30,000 - 50,000 gals – 30”- 36” tank

Another rule of thumb is to buy 1.5 sq ft of filter area per 10,000 gallons of pool water. The 3.1 sq ft sand filter (24” tank) is the standard size for most inground pools. Larger pools, (over 30,000), should use a 4.9 sq ft. sand filter (30” tank). Hayward makes a 27” sand pool filter, which has 3.7 sq ft of filter area. Pools over 50,000 gals should install a 36” tank, with over 7 sq ft of surface area.

With sand pool filters, bigger is always better (not true for pool pumps). The more square footage of filter area, the longer the time will be in between cleanings, and the faster adverse water is cleaned up. In fact, larger filters can prevent most adverse water conditions in the first place.

Aside from pool size in gallons, other factors include the amount of debris the pool will receive and the usage of the pool. Dirtier and more active pools need more filtration, from larger filters.

Matching Sand Pool Filter to Pool Pump

Every sand filter has what is called a Design Flow Rate. This is listed under the performance data on pump product pages, as a GPM measure (gallons per minute). Knowing this info, you can look at your pool pump’s flow curve, or Pump Flow Chart, (on the pump product pages) to see how much flow rate to expect from your particular pump at an average amount of resistance, say 30 feet of head. It’s ok for a pump to be a little undersized, but don’t be oversized and buy a sand pool filter that has a smaller design flow rate than what your pump is capable of producing. If you push too much water into an undersized sand pool filter, the dirt trapping ability of the sand will be compromised and the sand will be damaged over time.

You don’t have to match manufacturer, by the way. A Hayward sand filter can be used just fine with a Pentair pool pump, or vice-versa, as long as the pump flow rates match the filter design flow rate.

One other factor that should influence your opinion is the availability of replacement parts. It may be best to purchase something by Jandy, Pentair or Hayward, with a large amount of parts in distribution. Smaller manufacturers may not have quick access to filter parts when you need them most. Beware of newer ‘knock-off’ sand pool filters, often sold for aboveground pools and small inground pools. Parts are next to impossible to obtain for these imported sand filter systems, which are designed to look like Hayward systems, but most parts are not interchangeable.

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