Your pool filter is the hardest-working part of your equipment pad. In the Phoenix area it fights three things most pools in the country don’t see all at once: very hard fill water, monsoon dust storms, and a swim season with about 111 days a year at or above 100°F. We’ve serviced Valley pools since June 2006. This guide covers how each filter type works, which one suits Valley water, how to keep it running month by month, and how to tell a cleaning problem from a repair.
Quick answer
- Cartridge filters typically trap particles down to about 10–20 microns, use no backwash water, and pair well with variable-speed pumps. For most Valley homes they’re the practical choice.
- DE filters trap the finest particles (about 3–5 microns) but need backwashing, fresh DE powder and periodic grid teardowns.
- Sand filters are the simplest, catch the largest particles (about 20–40 microns) and are cleaned by backwashing.
- Whatever you own, clean it by the pressure gauge: when it reads about 8–10 psi above its clean baseline.
What a pool filter does
Your pump pulls water from the skimmer and main drain, pushes it through the filter, and sends it back through the returns. The filter holds dust, pollen, sunscreen oils and dead algae so your chlorine isn’t wasted on them. The CDC recommends at least 1 ppm free chlorine and a pH of 7.2–7.8 for home pools. A dirty or damaged filter makes those numbers much harder to hold, because debris keeps eating chlorine that should be protecting the water.
The three filter types, compared
| Cartridge | DE | Sand | |
|---|---|---|---|
| Typical particle capture | ~10–20 microns | ~3–5 microns | ~20–40 microns |
| How it’s cleaned | Remove and hose off; periodic soak | Backwash, recharge DE; teardown of grids | Backwash; replace media when worn |
| Backwash water | None | Yes | Yes |
| Upkeep effort | Moderate, hands-on | Highest | Lowest day to day |
| Hard-water issue to watch | Calcium crust in the pleats | Scale and oils on grids | Sand clumping and channeling |
| Works with variable-speed pumps | Very well | Yes | Yes; check backwash flow |
Cartridge filters
Water passes through pleated polyester cartridges. Because there’s no backwash, you don’t send pool water down the drain every time you clean, which matters in a desert. Cleaning means shutting the pump off, relieving pressure, removing the cartridges and rinsing each pleat from top to bottom. Hard water makes a periodic cleaner soak important, because calcium and oils bind into the fabric and a hose alone won’t lift them.
DE (diatomaceous earth) filters
DE filters coat a set of fabric grids with a fine powder made from fossilized diatoms. That powder traps the smallest particles of any residential filter. The trade-off is maintenance: backwash, add fresh DE afterward, and tear the filter down periodically to clean the grids. A torn grid or cracked manifold lets DE blow back into the pool, where it shows up as fine gray dust on the floor near the returns.
Sand filters
Water flows down through a bed of filter-grade sand, and you clean it by reversing the flow (backwashing). It’s the simplest system to run, but it passes the finest particles, and over time the sand wears smooth, clumps or channels so water finds a path around it. Sand coming back into the pool usually points to a broken lateral at the bottom of the tank.
Why Valley water is hard on filters
The USGS classes water above 180 mg/L (about 10.5 grains per gallon) as “very hard.” Every Valley water provider below publishes a range that reaches that level:
- Chandler: 10.1–16.8 gpg (173–288 mg/L), City of Chandler 2025 Water Quality Report.
- Mesa: 12–22 gpg depending on the water source serving your area, City of Mesa.
- Queen Creek: 6–17 gpg, Town of Queen Creek.
- Phoenix: 10–17.6 gpg (172–302 mg/L), City of Phoenix 2025 Water Quality Report.
- Scottsdale: about 13–17 gpg depending on area, Scottsdale Water 2025 Water Quality Report.
Hard water isn’t a health issue, but it matters for your pool because pools lose water to evaporation every day and get topped off with fresh, mineral-rich water. The water evaporates; the calcium stays. That calcium builds up in cartridge pleats, on DE grids and in sand beds, raising your filter pressure sooner and shortening how long the media lasts. This is why a filter cleaning in the Valley often needs a soak or descaling step, not just a rinse.
Which filter fits a Valley pool?
| If this describes you… | Usually the better fit | Why |
|---|---|---|
| You want to save water and have a variable-speed pump | Cartridge | No backwash water; performs well at low flow |
| Clarity is your top priority and you don’t mind upkeep | DE | Finest filtration of the three |
| You want the simplest routine and have a place to backwash | Sand | Backwash and go |
| Your current filter works and is sized right | Keep it | Changing types is rarely worth it on its own |
| Your tank is cracked or the filter is undersized for your pump | Replace, and choose by the rows above | A repair won’t fix a sizing or tank problem |
A Phoenix filter calendar, month by month
The calendar below is built on NOAA’s Phoenix climate normals and the National Weather Service’s official monsoon season (June 15 to September 30). Your pool’s exact schedule depends on trees, bather load and pump runtime, so let the pressure gauge have the final say.
| Months | What the weather is doing | What to do with your filter |
|---|---|---|
| Dec–Feb | Average highs in the mid-60s to about 71°F; no 100°F days | Good time for a deep clean, cartridge soak or DE teardown. Inspect for torn pleats, cracked lids and worn o-rings. |
| Mar–Apr | Highs climb from about 78°F to 86°F; spring wind | Record a fresh clean-pressure baseline. Check after windy days. |
| May | Highs near 95°F; about 9 days at or above 100°F on average | Get the filter in top shape before summer. Replace worn cartridges or spent sand now, not in July. |
| Jun | Highs about 104°F; about 25 days at or above 100°F; monsoon starts June 15 | Check pressure weekly. Expect faster buildup as swim use and chlorine demand rise. |
| Jul–Aug | Highs about 105–107°F; 27–29 days at or above 100°F; the wettest months of the summer | Check the gauge and baskets after every dust storm or rain. Clean as soon as pressure is 8–10 psi over baseline. |
| Sep | Highs about 100°F; monsoon ends September 30 | Keep weekly checks through the last storms; a full clean at the end of the month. |
| Oct–Nov | Highs drop from about 89°F to 77°F; leaves start falling | Watch skimmer baskets and pressure during leaf drop. |
Troubleshooting matrix
| What you see | Likely cause | What to try | Call us if… |
|---|---|---|---|
| Pressure high and flow weak | Dirty media, full baskets | Clean baskets, then clean or backwash the filter | Pressure stays high right after cleaning |
| Pressure high right after a cleaning | Calcium or oils bound in the media; worn cartridge; closed or partly closed valve | Soak cartridges in a cleaner or descaler; check valve positions | The media is old or damaged |
| Pressure lower than normal | Clog before the filter (basket, impeller), air leak, low water level | Check water level, baskets and the pump lid o-ring | The pump is loud or losing prime |
| Cloudy water with good chemistry | Filter not running long enough; torn media; channeled sand | Run the pump longer; inspect the media | It’s still cloudy after cleaning and longer runtime |
| Sand or DE in the pool | Broken lateral (sand) or torn grid/cracked manifold (DE) | Stop and inspect the filter internals | Almost always; these are part replacements |
| Water leaking at the filter | Lid o-ring, clamp, drain plug or a cracked tank | Turn off the pump; check the o-ring and clamp | The tank or lid is cracked; don’t run a cracked filter under pressure |
| Air bubbles from the returns | Air leak on the suction side, low water, loose pump lid | Top off water; check the pump lid seal | It continues after those checks |
How to clean your filter safely
- Turn the pump off at the timer or breaker.
- Open the air relief valve to release pressure before loosening any clamp or lid.
- Cartridge: remove the cartridges and rinse each pleat top to bottom. For calcium crust or greasy buildup, soak in a cartridge cleaner per the label, then rinse.
- Sand: with the pump off, set the valve to backwash, run until the sight glass clears, then rinse briefly and return to filter. Never move a multiport valve while the pump is running.
- DE: backwash, then add the amount of DE your filter’s manual specifies through the skimmer. Tear down and clean the grids on the schedule in your manual.
- Reassemble, open the air relief, restart, close the relief when water sprays steadily, and write down your new clean-pressure reading.
What we check on a filter service call
When we look at a filter, we start with the gauge reading against its clean baseline, then open the filter and check the media for calcium crust, tears, flattened pleats or worn sand. We check lids, clamps and o-rings for leaks, look at the valve and air relief, and confirm the filter is the right size for your pump. Many filter problems are a part, like a lid, o-ring, valve, cartridge or grid, rather than a whole new filter.
Repair or replace?
Filter repair typically runs $50–$800, depending on the part and the filter type. A repair usually makes sense when the tank is sound and the problem is a part or worn media. Replacement usually makes more sense when the tank or body is cracked, the filter is undersized for your pump, or repeated repairs are adding up. See our pool filter repair page for how we diagnose it.
Frequently asked questions
How often should I clean my pool filter in Phoenix?
Clean or backwash when the pressure gauge reads about 8–10 psi above its clean baseline. In June through September, and after monsoon storms, that happens more often than in winter.
Which pool filter is best for Arizona?
Cartridge filters suit most Valley pools because they use no backwash water and pair well with variable-speed pumps. DE filters give the finest filtration with more upkeep, and sand is the simplest to run.
Does hard water affect my pool filter?
Yes. Valley cities such as Chandler, Mesa and Phoenix publish hardness ranges that reach the USGS “very hard” level. As pool water evaporates and is topped off, calcium builds up in the filter media, so cartridges and grids need periodic soaking or descaling.
Why is my filter pressure still high after cleaning?
Usually calcium or oils are bound into the media, the cartridge is worn out, or a valve is partly closed. Soak the media in a cleaner and check valve positions; if the pressure stays high, the media may need replacement.
Why is sand or DE coming back into my pool?
Sand in the pool usually means a broken lateral in a sand filter. DE in the pool usually means a torn grid or a cracked manifold. Both need a repair.
How much does pool filter repair cost?
Typically $50–$800, depending on the part and filter type. We give a free quote after diagnosing the filter.
Should I switch filter types?
Usually not if your current filter works and is sized correctly. Switching makes more sense when the existing filter needs replacing anyway.
Want an expert look at your filter? Contact AZ Oasis Pools or call 480-694-1158 for a free quote, or ask about weekly pool maintenance with filter checks included.