Swimming Pool Filters, Sand, DE, and Cartridge filters
Trying to decide on which type of filter to buy?
There are three main types of swimming pool filters, D.E. (which stands for Diatomaceous Earth) {first filter}, Sand {middle filter} and Cartridge {last filter}. Different regions of the country seem to have different preferences; personally my order would have D.E. first, then Sand, then cartridge filters. However, the suitability of a filter to a pool can have more to do with size, than with type. Always go at least one size larger than you think you need. Buy the largest filter you can afford, it’s money well spent.
Even though I have just stated a preference of D.E. filters over Sand over Cartridge filters, I would rather have a large cartridge filter than a small D.E. filter. So remember, in pool filters, size matters! Many filters installed in the 70’s and 80’s were much too small for the size of pool they filter, and with the deterioration of age are just barely operating. Major manufacturers try really hard to produce no “junk.” So once again, filter size is more important than brand, name, type, color, etc.
Sand filters
The sand in a 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 its clean, start-up reading, it is time to backwash the captured dirt out of the filter.
“They say” that a sand bed should be replaced after seven years. Gradual loss of efficiency may be hard to notice. If your filter requires frequent backwashing, every week or two, the sand bed may be “mudballed”, or it may be “channeled”. It may also “calcify” with calcium deposits. Other water balance problems may also contribute to sand deterioration, but a properly sized filter could go over 10 years between sand changes.
Use of Biguanide chemicals, i.e., Soft Swim or Baquacil require annual cleaning of the sand to prevent it from “gumming-up”. High amounts of bather oils can gum-up a sand bed. And just the years of a pump forcing water over the grains wears away the sharp edges of the sand. Such sand becomes more circular, and traps dirt less efficiently.
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. So, if you’ve kept very good chemical maintenance and your circulation is good, you may have a filter problem. Is the filter sized properly? Many filters of the 70’s – 80’s were grossly undersized, the trend now in pool filtration is “Go Big Early.”
Adding a small amount of aluminum sulfate or “alum”, 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 or other filter media.
“How and When do I Backwash my Sand Filter”
When the pressure gauge is reading 8 – 10 lbs above the clean, starting pressure (after backwashing), it is time to backwash the filter. 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.” Sand filters can have either a push-pull valve (also known as a slide valve) or a multiport valve. The multiport valve has multi-ports on the valve, usually 6 positions:
- FILTER: Keep it here 99%, except when backwashing, rinsing or wasting
- RINSE: Use this setting for 20 seconds after backwashing to rinse tank
- RECIRCULATE: Use this if the filter’s broken; at least you’re circulating.
- BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out
- CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position
- 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.
So, to backwash a sand filter with a multiport valve;
- Shut off pump motor
- Press down on valve handle, rotate valve from FILTER to BACKWASH position
- Roll out any backwash hose or open any waste line valves
- Open air bleeder assembly on filter, and turn pump on.
- Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly
- After hose fills with water, run for 2 – 3 minutes or until water runs clear
- Shut off pump motor and move multiport valve handle to RINSE position Run on rinse for 15 – 25 seconds.
- Shut off pump motor and move multiport valve handle to FILTER position
- Turn pump back on and note lower pressure. Roll up backwash hose
To Backwash a sand filter with a slide 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″
- Open air bleeder assembly on filter, and turn pump on
- Watch pressure gauge for backpressure (+ 40 PSI) and hose for kinks. Be prepared to shut off pump quickly
- After hose fills with water, run 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. Roll up backwash hose
A properly sized sand filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashings. A “Filter Run” of less than 4 weeks may indicate sand problems (or sizing problems).
Sand in the pool?
Bad news. If it hasn’t blown in, or been carried in on the feet of swimmers, it’s 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 fresh sand and test.
Sand bed replacement:
To replace filter sand, you’ll first need to empty out the existing sand. One method is to spread a tarp out beneath the filter drain assembly. Then remove the entire assembly, turn on the pump, and step back! The water pumping through the filter will remove most of the sand out the drain hole. Another method 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 octagonal dome wrench to remove the dome. Once the dome is removed, gently twist the baffle/pipe out of the way 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. You can reconnect them later with unions or couplings. Once these pipes are cut, the clamp band connecting the valve to the filter is removed, and the valve pulls straight up and off. Plug or tape or cover 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 small cup to scoop out the sand.
Be very careful as you scoop or suck, not to knock or break the laterals at the bottom of the tank. They can be brittle when the get older, and it may be wise 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, so the new sand pouring in won’t crack them. Again, if you have the top mounted multiport, cover the standpipe opening. 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 it in! Use only specially graded pool filter sand; #20 silica sand, 45 – 55 mm. On top mounted multiport filters, use care to keep the lateral/ hub assembly 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 the sand is added.
Add the recommended amount of sand only; more is not better! If you don’t know this info, contact your dealer or manufacturer. Most tanks are filled only about 2/3 of the way full, to leave enough “freeboard” space on top. When full, lube o-rings and reassemble filter top. Make sure 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.
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.
Leaking filter?
Sand filter tanks rarely leak themselves, however leaks often occur in and around the multiport interface. A common complaint is that water is leaking out of the backwash port of the multiport (six position) valve. Slight adjustments of the handle may temporarily solve this problem. A more permanent repair may necessitate replacement of the spider gasket inside of the multiport. You may also have leakage up around the middle of the handle on the valve, which external adjustments rarely fix. This usually requires replacement of a Teflon washer and sometimes the spring as well.
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. This is a easy inspection 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 secured tightly or properly sealed.
Leaking valve repair:
Usually a one hour job, plus internal valve components; gaskets or springs.
Filter replacement?
Well, they don’t last forever. But almost. A new filter may be in order if your current filter is outdated (15 – 20 yrs old) and 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.
Sand filter replacement:
Price is size dependent, however, as an example, we sell the Pentair Tagelus TA-60D filter for $294.97.
Diatomaceous Earth (D.E.)
The D.E. filter is the most efficient type of pool filter on the market. It can trap particles down to 3 – 5 microns; well below what the naked eye can see. As with sand filters, the pressure gauge indicates a need for backwashing when it reads 8 – 10 lbs. higher than its clean reading. After backwashing a D.E. filter, a new application of D.E. filter powder is added to the filter by pouring into the skimmer. An annual breakdown of the filter is necessary to thoroughly clean D.E. filter grids.
A D.E. filter requires that the operator (you) add D.E. powder to coat the filter grids inside of the filter tank. This widely available, inexpensive powder is actually the microscopic skeletons of Diatoms, an ancient, sub aquatic creature. Under the microscope, these skeletons appear to be tiny sponges. This is where the dirt gets trapped in your filter. The powder, which is added at your skimmer, dissolves in the pipe on its way to the filter tank. When it reaches the grids, which are covered with a nylon type of fabric, the powder stops, coating the grid. Grids are also called Elements or Septums. The water continues to pass through, first through the powder, then the fabric covered grid. As the water passes through the D.E. and enters the grid it leaves the dirt, trapped in the D.E. powder “cake” or coating.
The D.E. powder is what filters your pool water in a D.E. filter. Do not operate your pump without having the D.E. powder coating the grids, or you will see your pressure rise very quickly, and if left in this manner the grids could become damaged. As the pressure gauge on a D.E. filter increases, flow rate decreases. Eventually the flow rate will allow the water quality to suffer. You will need to backwash the filter to remove the D.E. that is clogged up with the dirt. After backwashing thoroughly, add new D.E. powder to the filter through the skimmer. If using biguanides (Soft Swim or Baquacil) you will need twice annual, very thorough cleaning to prevent it from gumming up. All D.E. filters should have this done at least once per year. Thorough cleaning is accomplished by turning the pump off and draining the filter. Remove the tank top half, and remove the grid assembly. Hose the grid assembly thoroughly. If you want to do an extra good job, after hosing, soak the assembly in a trash can filled with water and a filter cleaner product. (or use TSP {trisodium-phosphate} from the hardware store). Rinse thoroughly before reinstalling grids into tank.
When backwashing a D.E. filter, do the “process” several times. That is, backwash until water runs clear, move the multiport valve to FILTER and run it on filter for a 5 – 10 seconds, and backwash again until it runs clear, etc…do this 2 – 4 times. Remember to always shut off the pump before turning your multiport valve or your push-pull valve. Each time you go through the cycle of filter/ backwash/ filter, you will get more dirt/ D.E. out of the filter, giving you a better, more thorough backwash.
Also important in ensuring an effective backwashing is to make sure skimmer baskets and pump baskets are clean to allow for full flow entering the filter
How do I Backwash my DE Filter?
When the pressure gauge is reading 8 – 10 lbs above the clean, starting pressure (after backwashing), it is time to backwash the filter. 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.” Sand filters can have either a push-pull valve (also known as slide valves) or a multiport valve. The multiport valve has multi-ports on the valve, usually 6 positions:
- FILTER: Keep it here 99%, except when backwashing, rinsing or wasting
- RINSE: Use this setting for 20 seconds after backwashing to rinse tank
- RECIRCULATE: Use this if the filter’s broken; at least you’re circulating.
- BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out
- CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position
- WASTE/ DRAIN: Another filter bypass setting, but this one sends the water out of the waste pipe (hose), instead of returning it to the pool. Used to lower pool water level or to vacuum to waste
So, to backwash a D.E. filter with a multiport valve;
- Shut off pump motor
- Press down on valve handle, rotate valve from FILTER to BACKWASH position
- Roll out any backwash hose or open any waste line valves
- Open air bleeder assembly on filter, and turn pump on.
- Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly
- After hose fills with water, run for 2 – 3 minutes or until water runs clear
- Shut off pump motor and move multiport valve handle to RINSE position. Run on rinse for 5 – 10 seconds. Shut off pump again, and move handle back to BACKWASH. Turn on pump again until water runs clear. Continue in this fashion 3 – 4 times, alternating between Backwash & Rinse, to ensure a thorough backwash.
- Shut off pump motor and move multiport valve handle to FILTER position
- Turn pump back on and note lower pressure. Roll up backwash hose
- Add 1 lb D.E. powder per 10 sq ft of filter area. Look on filter tank
To Backwash a DE filter with a slide 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″
- Open air bleeder assembly on filter, and turn pump on
- Watch pressure gauge for backpressure (+ 40 PSI) and hose for kinks. Be prepared to shut off pump quickly.
- After hose fills with water, run for 1 – 2 minutes or until water runs clear. Shut off and push handle back down. Turn pump on and run in filter position for 15 seconds and then shut pump off and backwash again for 1 min. Filter again for 15 seconds and another 30 second backwash.
- Shut off pump motor and push T-handle back down into locked position
- Turn pump back on and note lower pressure. Roll up backwash hose
- Add 1 lb D.E. powder per 10 sq ft of filter area. Look on filter tank.
A properly sized D.E. filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashings. A “Filter Run” of less than 4 weeks may indicate grid problems (or sizing problems). Filter grid fabric can become clogged with Calcium deposits or oils. After removing the grids from the assembly, you can soak in TSP (trisodium-phosphate) and warm water to remove oily deposits. If you use Baquacil or SoftSwim, and you can soak the grids in a 10% muriatic acid solution for a few minutes followed by a full rinse. TSP soak and Rinse will remove mineral deposits such as Calcium.
D.E. powder in the pool?
You either have holes in the fabric of the grids, or a crack in the manifold that the grids attach to. It can also mean a broken air bleeder tube or assembly. Finally, D.E. in the pool can mean that the multiport or push-pull valve is allowing powder to bypass the filter. You will notice this most when adding new D.E. powder after backwashing, but you can test this at any time. The best method to determine the cause is to remove the grids and clean/ inspect thoroughly.
Filter Grid replacement:
Grids and manifolds vary by manufacturer, and can be expensive. $25 per grid; up to $100 for a manifold. Labor is usually under one hour.
If handy with an awl, torn grids can be sewn instead of replaced.
Poor water Quality?
It could be a problem with your multiport or push-pull valve. The valve could be allowing water to bypass the filter and return to the pool unfiltered. Perhaps you are not running the filter long enough. Perhaps there is not enough D.E. powder in the filter, or too much. You may also need to backwash the filter or remove the grids and clean them manually. Poor sanitation, poor water balance, and pool circulation could be another cause, and it could have nothing to do with the filtering at all. Remember: filtration + sanitation + circulation = 
How long should I run my filter each day?
Well, just as much as you need. Careful experimentation will show you when the water quality begins to suffer. Many people with smaller, older equipment (filter/ pump) run their systems 24 hours per day. The average (I would guess) would be about 16 hours. BUT! It depends on your system. Undersized? Old? High pool Use? Large Debris Load? Heavy Sunlight? Any of these factors call for extra filtering. If you’re too frugal with the electricity, you may have to pay more in chemical costs.
Leaking filter?
Most D.E. filters have a belly band clamp with a large O-ring between tank halves. The o-ring can become distended or flattened and may need to be replaced if water is dripping from the center clamp. Caution: Do Not remove the center clamp while the pump is running, and without first releasing pressure inside the tank. You may notice your multiport valve leaking in one or more areas. See sand filter info on previous page. If your push-pull valve is leaking out of the backwash port (where the hose attaches), the plunger either needs replacement, or a new set of o-rings.
Plunger replacement:
Varies by manufacturer. Around $90, plus 1 hour labor.
Filter replacement:
D.E. filters are more expensive than sand filters. You may want to replace if your filter is old and tired, or you may decide to upgrade efficiency from a sand or cartridge filter. Price varies by manufacturer; however, as an example, we sell the Pentair FNSP 48 for $479.97.
Cartridge filters:
Filter of choice for most spas, and many smaller above ground pools, the cartridge filter is enjoying a resurgence in popularity. The cartridge filter element, an aquatic version of the pleated air cleaner in your car, traps dirt and particles of 25 – 100 microns in size. The cartridge is removed from the tank and hosed thoroughly, top to bottom, with a high pressure hose to remove dirt when the pressure gauge rises 8 – 10 lbs. above its clean reading. I know some people that take their cartridges to the local self serve car wash place for cleaning. Each time the filter is cleaned, some of its filtering ability is reduced. The cartridge should be replaced every 2 – 5 yrs, depending on the work it was asked to do. If the filter was a bit undersized, and had some algae every year and lots of tree debris, etc. then it may last only 1 – 2 years. Nicely sized cartridge filters can operate for 6 months between cleanings.
“How do I Backwash my Cartridge Filter?
A trick question. There is no backwash valve on a cartridge filter because today’s pool filter cartridges aren’t built for backwards flow. Instead, the pump is shut off, air bleeder opened, lid removed, cartridge removed, hosed thoroughly top to bottom, and replaced. It’s a bit of a pain to do, but hopefully the filter is sized so that it’s a 1 – 2 x per year job. Another advantage is that cartridge cleaning doesn’t waste as much water as backwashing.
Soaking the cartridge in a TSP (trisodium-phosphate) or similar solution prior to hosing will improve your cleaning. Do not use TSP if you utilize Baquacil or Soft Swim for sanitation.
Use of a clarifier or Chitin product like Sea-Klear is a great help to a cartridge filter. Some people also increase the filter efficacy by adding a small amount of synthetic filter aid powder (1 – 2 cups) through skimmer. D.E. powder is not recommended by most manufacturers, as it can clog the pores of the cartridge.
Disposal/replacement of the cartridge, its difficulty in maintenance (no backwashing), and its low efficiency are the reasons I don’t recommend these filters for use in most larger swimming pools. But for pools under 30,000 gals., there are some nice filters like the Hayward C-4000 that can really be a great filter.
Filter Cartridge Replacement:
Right off the shelf for $40 – $100, depending on its size. No professional labor needed.