Beginner's Guide to Swimming Pool Filters

Spring rains have subsided, lawns and gardens have been the primary focus of attention. The garage is even getting somewhat organized, and as the days start to finally promise some consecutive sunshine you turn to the last but not least most important thing in the yard that’s often the final spring project for many homeowners: the swimming pool!

Some folks are lucky. The pump primes right up, water circulates, there are no leaks, and they are off to good start. For others, a common fate is shared as they open to a non-working pump, cracked or damaged filters, or just now remember the previous season’s struggle with a filter system that was just not doing the job anymore.

If you are still struggling to clear the pool water, here's information that can be useful to you, our Beginner's Guide to Pool Filters.

Filtration, Filtration, Filtration

To help you comprehend, I first must exude a pool pro’s wisdom with the mantra: “Filtration, filtration, filtration!” as this is the true secret to keeping a pool clear!

The pump and filter system is the heart of your pool and it does most of the cleaning and clarifying, so make sure it’s functioning well and sized properly.

There are a variety of filter brands and models for every size pool, in-ground and aboveground alike. Some great brands are Hayward, Pentair, Jandy, and Waterway and they are sold as filter only or as a system with a pump.

Aboveground systems usually include hoses and fittings, a pump, and base so they are a “plug and play” purchase. For smaller pools and soft-sided pools there are some nice products from Intex and GAME that are easy on the budget, too.

Generally, they all carry similar warranties and have the same basic features and functions. You just need to place your faith in a brand and go for it like you would if you were choosing any other household appliance like a new stove.

What I have found is that most folks replace their old one with the same type and/or brand that was there when they bought the home, buy the same kind their parents had, or take a tip from a friend or neighbor. By the way, your pump and filter can be different brands, no problem there.

A good source of pool filter advice (outside of mine) would be to ask any one of these people, read some good pool blogs, manufacturer sites, and/or read some real reviews on line.

So let’s dive into the details of the three main types of swimming pool filters, sand, cartridge, and DE, and distill some differences.

SAND FILTERS

A sand filter is comprises a hollow tank on a stand with a simple vertical PVC pipe stand in the center that extends to the bottom and is fitted into a manifold with slotted lateral pipes extending in a fanned out fashion looking much like wagon wheel spokes on an axle tipped on end.

Sand filters are filled with, you guessed it, sand, but not just any sand. You can fill it with a Pool Filter Sand, (#20 grade silica sand for pools at $4.99-$9.99/50 lbs.), Zeolite (a premium high porosity filter media at $39.99/50 lbs.), or Filter Glass (recycled crushed glass that actually filters out blood cells and entraps cryptosporidium at $44.99/50 lbs.).

Traditionally, Sand Filters are filled 2/3 full and a handy multiport valve sits on top with an O-ring and a clamp band to seal and secure the valve to the filter. The multiport valve allows you to control all of the filter functions externally.

Note that variable valves vary. Try to say that 10 times in a row! Some models have a threaded top mount valve or a side-mounted one that is fixed to the side of the tank via two bulkhead unions. They can have 1.5-inch ports or have 2" ports.

Multiport valves, also used on DE filters, typically have six positions but can have from four to eight. They are set to “filter” mode most of the time. You can use the valve to recirculate, vacuuming to waste, or to drop your water level for closing. Check your owner’s manual for full functionality and closing recommendations.

How it all works: Water flows through the valve and diffuser, passes through the sand bed, which captures fine debris particulates, and travels through the slotted laterals up through the standpipe and goes back to the pool.

As the sand bed slowly plugs up, your pressure gauge, located on the valve (or dome for side mounts) will rise in pressure. Keep in mind that the more a sand filter plugs up, the finer the particulates that are captured so it’s good to let it plug up somewhat, and not backwash too frequently.

Normal operating pressure depends on your pump size and overall resistance in the system, but most residential tanks will start at between 10-20 psi and when the pressure rises 8-10 pounds, it is time to backwash the filter.

To backwash a sand filter, cut the power to the pump and reverse the valve, then turn the pump back on. The water flows in reverse and dirty water is sent out another port on the valve, where you will have attached a backwash hose with a clamp and flushed to the lawn, or wherever your backwash hose may lead.

Just make sure it goes away from the pool and, if heavily chlorinated, away from any flowers or gardens. It is best to do this when your chlorine or sanitizer is low so you don’t waste it! Flushing for two minutes or so should do it or you can watch the discharge water or sight glass on the valve until the water runs clear. Shut the pump off and return the valve to filter mode.

Sand will filter down to about 20 microns (1 micron is equal to 10-100 human hair widths) and should be replaced every three to five years. Smaller tanks may be emptied at the end of the season so it is easy to store away the filter and then replaced with fresh sand each spring. Winterizing involves a heavy backwash then simply draining the tank by unscrewing a plug at the bottom and putting the valve in “winterize” position to drain the valve itself.

You will know the filter is working if the water pressure coming into the pool is strong, the pump basket housing is always full of water, the gauge pressure is normal, and the pool water stays clear.

Top Mount Sand Filters vs. Side Mount Sand Filters

Top mounted sand filters are always sold with a multiport valve that is flange attached to the top of the filter tank. Top mount sand filters also include all internals (standpipe, hub, laterals), and the drain assembly. Top mount sand filters are cheaper for manufacturers to make, because the top-mount design is simpler, and much fewer parts are used.

1. Top mounted multiport valve can be rotated to align with pump and other equipment.
2. Lower cost filters;  from reduced cost of manufacturing top mount sand filters.
3. Fewer parts than side mounted tanks; no bulkheads or top closure assembly.

Side mounted sand filters are sold separately from the valve, a multiport or slide valve, primarily because you have a choice. A slide valve (aka push-pull valve) offers only two functions, filter or backwash, but can be preferred because of (much) lower resistance than a multiport valve, and because the simple design requires fewer repairs.

1. Side mount filters are NSF certified for commercial pools to NSF/ANSI Standard 50.
2. Side mount filters can use a slide valve for higher flow rates and reduced restriction.
3. Side mount filters provide easier access to inspect sand and service internal parts.

Sand Bed Rejuvenation: You can clean your sand or zeolite with a quart of Filter Sand cleaner to disinfect the media, decalcify, and rejuvenate the bed.

Filter Sand Change: To empty or change the sand you simply disconnect the hoses or PVC, remove the valve, and carefully remove scoop by scoop with a coffee mug or soup can. When you’ve removed most of the sand, the standpipe and lateral assembly can be folded up or unscrewed and removed so that you can use a bigger scoop and eventually tip over the tank and rinse it out. Then replace the inner components, center and cover the pipe so sand does not get in it, add enough water to cover the laterals, and replace with new sand. Remove the cover, clamp on the valve and you are good to go!

Sand Filter Parts: Commonly replaced filter parts would include drain assembly parts or laterals. Sand filters have very few parts, which make them simpler to work on than DE filters.

CARTRIDGE POOL FILTERS

For those who want more simplicity than the aforementioned filtration apparatus, and a worry-free setup, the cartridge filter may the way to go! This style of filter has taken the aboveground market by storm due to its simple design and ease of use.

Many cartridge filters are tall and narrow so they save on space and, unlike sand, the filter is a simple two-piece tank (lid and bottom). They use a spun, bonded polyester, fan folded filter much like a cylindrical automotive air filter.

Cartridge filters have the most available filter surface area, ranging from 50-500 square feet. The cartridge has less resistance so you get more turnover in gallons over the same horsepower with sand, with less strain on your pump. This also means you can run it for fewer hours and save electricity and money! Some filter cartridges are also available in an antimicrobial version: Microban.

Here’s how they work: Water is pushed into the filter tank from your pump and flows through the filter membrane. Fine particles and debris are trapped in the fabric and clean water returns back to the pool. A gauge on top lets you know when it’s time to clean.

When the pressure swings up 10 points or so it is time to remove the cartridge and you just hose it down. No backwashing means you save on heated and chemically treated water too, although you do have to spend some time if you want to really deep clean between the pleats. There are also some nice tools you can buy that fit on your garden hose just for this.

A cartridge filter tank comes apart with a belly clamp or knob on the top. For aboveground pool owners, be sure to close off the skimmer and return jets before you open the tank or you will have a water gusher. Some systems come with shut off valves to prevent this or you can add them yourself. Slice, gate, or ball valves work great.

Cartridge Rejuvenation: Occasionally, the cartridge needs more than a hosing. Soak it overnight in a large bucket of water and cartridge cleaner. If your bucket is not deep enough, just flip the filter over and repeat. Filter cleaners can restore the cartridge to its original white condition, and remove oils and mineral deposits.

Cartridge Replacement: The cartridge will last for one to three seasons depending on how many hours of use and how much cleaning it must do, but eventually they become fuzzy, the support straps break, and they either collapse or just get too stained and dirty to keep clean.

Many folks buy a new cartridge every few years and keep the old one just for spring cleanup. Replacing a cartridge is a back saver and much easier than all that sand! Replacement filters average about 75 cents a square foot and are easy to find on line or in most pool stores.

Cartridge Filter Parts: Commonly replaced parts include the tank lid O-ring, gauge, and cartridges. Since there is no multiport valve, cartridge filters often need the least amount of repair parts of all filter types.

DE POOL FILTERS

And in the spirit of saving the best for last, we have the Diatomaceous Earth filter! If you can’t pronounce it you can just call it DE!

DE powder is a fine natural powder composed of the fossilized exoskeletons of tiny diatoms that once thrived in the sea and are now layered underground. DE particles are hollow with high porosity so they make an excellent filter media.

Grids are held in place by a top and bottom manifold while the fingers are sandwiched between two pressure plates and a diaphragm gasket that allows the tubes to be shaken, but not stirred (haha, couldn’t resist that one!).

The amount of available filter area for DE filters falls between sand and cartridge from 24-60 square feet. Your manual will tell you how much DE to add based on the mode, which is normally 1 pound of DE for each 5 square feet of filter area.

Here’s how they work: Sprinkle the powder into your skimmer, which draws it into the filter and coats either fabric coated grids or a cluster of “fingers” with a fine layered top coat. A pound of DE goes for about $1.00 and is usually sold in 25 lb. bags.

DE powder is fine enough to let water pass through but almost nothing else! By using a DE filter you filter down below 5 microns and actually achieve a whole different level of water clarity: crystal clear water. But there is a downside in that spring startup can be a chore because the media is so fine it plugs up quickly and regularly and you will go through a good supply of DE if your pool is quite dirty or has experienced an algae bloom.

But let it be known that these trusty filters are designed for this and you simply bump and shake the debris from the fingers with the top mounted bump handle on most models or use the multiport valve on the grid style filters to just backwash out the collected debris. Either way it gets flushed away through a valve at the bottom of the tank or backwash hose, and you can re-add DE to the skimmer and the cycle starts over again.

DE Filter Rejuvenation: DE filter grids and fingers need periodic soaking just like a cartridge, especially in cases where the water is hard and the pores can calcify. DE filter cleaner is readily available to remedy this and the components are accessible by loosening a belly ring or unbolting the lid and separating the top half of the tank from the bottom. Again, shut-off valves are helpful for above ground cleanouts whereas in ground equipment owners should have no worries unless the top of the tank is situated below the pool water level. Grids and finger “nests” can be soaked overnight in a pail with the cleaner, then rinsed with a hose and replaced in the tank.

DE Grid Replacement: Grids can last up to 10 years, but eventually they may become ripped and torn, or the plastic beneath the fabric can break. Of all filter types, however, DE filter media can be the longest lasting.

DE Filter Parts: Common replacement parts are E-clips, O-rings, gauge, tank O-ring, and over time you may need to replace filter grids or fingers. DE filters have the most parts of all filter types, so may require a few extra repairs.

DO I NEED A NEW FILTER?

Start with your eyes and ears. If the pump is whining, grinding, corroded, or sucking air and your filter is leaking at the ports, just not keeping the pool clear, or it looks physically worn, it may be time for a new one. If a pump lasts 10 years, that is excellent!

A filter tank can theoretically last forever, but chemicals, weather, UV rays, and age can take its toll. If you can keep your equipment covered or surrounded by a wall, that is the best way to protect your investment. My system is next to the garage and we added a simple roof on two supports so we have had the same filter (tank) since 1979! I've replaced the filter media many times, however.

Some filters are woefully undersized. If you are cleaning your filter more than once per month, it may be too small for your pool. If you have frequent battles with algae, cloudy water or difficulty managing water clarity, your filter could be too small or the filter media inside has become tired and needs replacement.

FINAL THOUGHTS

It would seem that the good old sand filter is easy enough to use with external controls and contains just a few parts. Operation is a snap when all you do is move a valve handle, and if you use the 20 grade silica sand, it is inexpensive but some work to change. Performance is good and you have just a few wear and tear parts with the valve itself.

The cartridge filter has the least amount of parts and is the second best method of filtration. The negative is the cost of replacing the cartridge and cleaning between the all those pleats can be tedious. But it’s a no-brainer how easy it is to use when you just plop in a cartridge and let it go!

DE filters, although they outclass the rest for producing sparkling clear water, are laden with parts, can be tedious and frustrating at startup, and let’s not forget that you must buy, store, and handle the DE powder. But that’s the price you pay for that over-the-top sparkling water clarity and for some it’s worth it!

No matter which type of filter you buy, here's a few maintenance tips that should not be ignored. Always lube your O-rings in the spring with pool O-ring lube, use Teflon tape on threaded fittings. At the end of the season, give your sand filter media, grids or fingers, and cartridges a good cleaning and be sure to remove all drain plugs when winterizing.

Using shut-off valves and unions between your various pieces of pool equipment. It makes cleaning, servicing, and replacement a snap!

Whichever filter you decide is best for you and your pool. A new “heart” for your system may be just the breath of fresh life your pool needs. All three filter types are in use in someone’s yard today — tried-and-true methods of keeping a pool clean and clear so you can spend your time swimming and enjoying your pool.