Every pool has a filter, and it’s one of the most important parts of the whole system. The pump moves the water. The chlorine kills germs. But the filter is what takes the dirt out and makes the water look clear.
There are three kinds of pool filters: cartridge, DE, and sand. If you’re buying a new one, replacing an old one, or just trying to figure out what’s on your equipment pad, it helps to know how each one works. Here’s what we’ve learned from cleaning and fixing all three kinds across the Valley, and which one we think works best for most Phoenix pools.
The Short Version
| Cartridge | DE | Sand | |
|---|---|---|---|
| How clean the water gets | Very good | Best | Good |
| How you clean it | Take it apart and hose off the cartridges | Backwash, add new DE, and take it apart once in a while | Backwash |
| Water used to clean | Low | Medium | High |
| Work to clean | Medium | Most | Least |
| What wears out | Cartridges | Grids | Sand |
| How common in Phoenix | Most common | Common | Less common |
If you don’t want to read the rest, here’s our take. For most homes in the Phoenix area, a cartridge filter is the best pick. It uses the least water, it does a good job, and it’s simple. DE is great if you want the clearest water possible and don’t mind more work. Sand is the easiest to live with day to day, but it’s the weakest at catching fine dust, and dust is a big deal here.
How to Tell What You Have
Walk out to your equipment pad and find the filter. It’s usually a tall tank next to the pump.
- A cartridge filter has a clamp band or a big lid on top, and usually no multiport valve. Open it up and you’ll see one or more round, pleated cartridges that look like giant air filters.
- A DE filter looks a lot like a cartridge filter from the outside. The difference is a backwash valve, and inside there’s a set of fabric-covered grids or “fingers” coated in white powder.
- A sand filter is usually a round tank with a big valve on top that has six or seven settings, like filter, backwash, rinse, and waste.
If you’re still not sure, look for a label on the tank. The brand and model number will tell you.
Cartridge Filters
This is the filter we see most in Phoenix, and there’s a good reason.
Water flows through pleated fabric cartridges. The pleats give the fabric a lot of surface area, so it can hold a lot of dirt before it needs cleaning. Cartridges catch smaller bits than sand does, so the water looks clearer.
There’s no backwashing. When the cartridges get dirty, you shut off the pump, open the tank, pull them out, and hose off every pleat. That takes time and a little effort, but it doesn’t send hundreds of gallons of pool water down the drain. In a desert where water costs money and every gallon counts, that matters.
The downsides: cleaning a cartridge filter is a real chore. Big ones can have four cartridges, and each one needs a good rinse. And cartridges wear out. Over the years the fabric thins, the pleats flatten, and the bands crack. When that happens, they need to be replaced. Hard water also leaves calcium in the fabric, which makes them clog faster. Some owners soak their cartridges in a cleaner once a year to break that up.
Who it’s best for: most homes in the Valley, and anyone who wants good water without wasting a lot of it.
DE Filters
DE stands for diatomaceous earth. It’s a white powder made from tiny fossils. Under a microscope, each grain looks like a little sponge full of holes. When you add it to the filter, it coats a set of fabric grids inside the tank. Water passes through that coating, and the DE traps dirt so fine you can’t see it.
That’s why DE filters give you the clearest water of the three. If you’ve ever seen a pool that looks like the water isn’t even there, there’s a good chance it has a DE filter.
The downsides: DE takes the most work. When the pressure goes up, you backwash it, then add fresh DE powder through the skimmer. A few times a year, the whole filter needs to come apart so the grids can be hosed off and checked for rips. A torn grid lets DE blow back into the pool, and you’ll see a fine white dust on the floor.
DE powder also needs care. Wear a dust mask when you pour it, since you don’t want to breathe it in. And used DE can’t just go anywhere. Valley cities have rules about where backwash water can go, so check yours before you backwash into the yard or street.
Who it’s best for: owners who want the clearest water possible and either don’t mind the upkeep or have someone else do it.
Sand Filters
Sand filters have been around the longest. Water flows down through a deep bed of special filter sand, and the sand traps the dirt. When the pressure gauge goes up, you turn the valve to backwash. Water runs up through the sand the other way and flushes the dirt out a waste line. Then you rinse and set it back to filter. That’s it.
The downsides: sand doesn’t catch fine dirt as well as the other two. After a dust storm, a pool with a sand filter can stay hazy longer. Backwashing also uses a lot of water, often a few hundred gallons each time. In the Valley, that water then has to be replaced, and the new water brings in more calcium.
The sand wears out too. Over the years the grains get smooth and round, and they stop grabbing dirt as well. Hard water can also turn the sand into clumps. Most sand needs to be changed every several years.
Some owners swap the sand for glass media or another filter material. These can catch smaller bits than plain sand and sometimes last longer. They cost more up front.
Who it’s best for: owners who want the least hands-on work and don’t mind slightly less sparkle.
What Phoenix Does to Filters
No matter which filter you have, a few things here make it work harder than it would in most places.
Dust storms. A haboob can drop a layer of fine silt across the whole pool in an hour. All of that ends up in the filter. After a big storm, you’ll often need to clean the filter early. Our post on pools turning green after a monsoon storm covers what to do the day after.
Hard water. Calcium builds up in cartridges, on DE grids, and in sand. It makes all three clog faster and wear out sooner. Keeping your water balanced helps. We keep calcium hardness between 200 and 400 ppm.
Long pump hours. In summer, pumps here run 8 to 12 hours a day. More water through the filter means more dirt caught and more cleaning.
Trees and desert plants. Palo verde blossoms, mesquite pods, and palm debris break down into tiny bits that get past the skimmer basket and into the filter.
How Often to Clean Each One
The best guide is the pressure gauge on top of the filter. Write down what it reads right after a cleaning. That’s your clean number. When it climbs about 8 to 10 PSI above that, it’s time.
As a rough guide for Phoenix pools:
- Cartridge: a full cleaning every few months, more often in summer or after storms
- DE: backwash when the pressure goes up, and a full teardown a few times a year
- Sand: backwash when the pressure goes up, often every few weeks in summer
If the pressure gauge is broken or stuck, replace it. It’s a cheap part, and it’s the only way to know what’s going on inside the tank.
Signs Your Filter Isn’t Doing Its Job
- The water looks dull or hazy even when the chlorine is good
- The pressure gauge stays high right after cleaning
- Dirt or white powder blows back into the pool from the returns
- The pump sounds strained, or flow from the jets is weak
- The heater won’t stay lit, since low flow trips its safety switch
That last one surprises people. A dirty filter can make other equipment act broken. If your heater won’t light, the filter is one of the first things to check. And if your water is hazy, our post on cloudy pool water walks through the other causes.
Can You Switch Filter Types?
Yes. People switch for all kinds of reasons. Some want to stop backwashing and save water. Some want clearer water. Some just hate cleaning cartridges.
When you switch, the new filter has to be sized to your pool and your pump. A filter that’s too small clogs fast and makes the pump work too hard. The plumbing at the pad usually needs some changes too, since each filter connects a little differently. It’s a good job to do when the old filter is worn out anyway.
Common Questions
Which filter gives the clearest water?
DE, by a little. A clean cartridge filter is close behind. Sand comes in third.
Which filter is cheapest to own?
Sand usually costs the least to buy and run, but you pay for it in water. Cartridge filters cost more for parts over time, since cartridges need replacing, but they save water. DE is in the middle, plus the cost of the powder.
Can I clean my own cartridges?
Yes. Shut off the pump, open the tank, and pull them out. Hose each one from the top down, working between the pleats. Don’t use a pressure washer. It can tear the fabric. Let them dry if you can, since a dry cartridge is easier to check for damage.
How long do cartridges last?
Often a couple of years in Phoenix, sometimes more. It depends on how dirty the pool gets, how often you clean them, and how hard your water is. When the fabric feels thin or the pleats are torn, replace them.
Do I need a bigger filter?
If you’re cleaning it all the time, maybe. A bigger filter holds more dirt between cleanings and lets water through more easily. It’s worth asking about when your current one wears out.
Need Help With Your Filter?
We clean, repair, and replace all three kinds of filters for homes all over the Phoenix area. If you’d rather not deal with it, see our pool filter cleaning and repair page or call (623) 526-4945.
