DE vs cartridge pool filters: which is better in Ohio?

DE stands for diatomaceous earth, a fine white powder made from the fossilized shells of tiny aquatic organisms called diatoms. Under a microscope each grain is full of holes. Inside a DE filter tank are grids or fabric-covered elements. When you add DE to the system, the pump carries the powder into the tank and it coats those grids. Pentair's manuals call this the precoat. The coating of DE, not the fabric, does the actual filtering.

As dirt builds up, water has a harder time getting through and the pressure on the filter's gauge climbs. Pentair's guidance for its DE filters is to backwash when the pressure reads about 10 psi above the clean starting pressure, or when you notice the flow dropping. Backwashing reverses the water through the filter, which knocks the dirty DE off the grids and sends it out the waste line. Then you add a fresh charge of DE through the skimmer and the filter is back to work.

Once or twice a season, backwashing is not enough. The filter gets opened and the grids are hosed off or soaked to remove oils and fine debris that backwashing leaves behind. Pentair also warns never to run a DE filter without the powder coating, because the bare fabric can be damaged.

A cartridge filter is a tank holding one or more pleated fabric cartridges, usually polyester. Water passes through the pleats and the dirt stays on the outside. The pleats pack a lot of surface area into a small tank, which is what lets a cartridge filter hold a lot of dirt between cleanings.

You clean it by shutting off the pump, relieving pressure, opening the tank, lifting the cartridges out and hosing them down. Pentair says to clean its cartridge filters when the gauge reads about 8 to 10 psi above the starting pressure. There is no backwash, no waste water from the filter, and no powder to buy or handle. Cartridges do wear out and need replacing every few seasons, and they benefit from an occasional soak in a filter cleaner to remove oils and scale.

DE, clearly. Pentair's own comparison puts DE filters at less than 5 microns, cartridge filters at 10 to 30 microns and sand filters at 20 to 100 microns. All three catch the dirt you can see. The difference shows up in very fine particles: the haze left by pollen, fine dust, dead algae or a clarifier treatment. A DE filter polishes that out, and the water looks sharper.

That polishing is one reason we put a DE filter on our standard packages. A fiberglass pool's smooth, glossy surface and our MicroBrite lights at night both show off clear water, and they show off cloudy water too.

Cartridge, for most owners. Cleaning a cartridge is a hose, a clean patch of driveway and maybe twenty minutes. A DE backwash is quick once you know the valve positions, but you have to add the right amount of new powder each time and deal with where the backwash water goes. DE powder is also a dust you should not breathe, so Pentair recommends a mask when handling or recharging it.

That said, many DE owners prefer their routine. Backwashing takes a few minutes without opening the tank, and a well-sized DE filter goes a good while between full teardowns. If you use our weekly pool service, the difference mostly disappears, because we handle it.

This is the part of DE ownership that people forget to plan. Every backwash sends dirty water and spent DE out of the filter's waste line. It should not run into the street, a storm drain or a creek. Diatomaceous earth and fine debris settle into streambeds and can clog the gravel fish need, which is why places like Sacramento County require backwash water to go to the sanitary sewer or to a vegetated area on your own property, and recommend a separation tank to catch the DE.

Rules vary by community, so check with your city or sewer district before you route a backwash line. On the pools we build, we plan the waste line during design, pointing it to a lawn area or bed well away from the pool, the house foundation, a neighbor's yard and any septic system. A separation tank, which catches the spent DE so you can bag it, is an option where lawn discharge is not a good fit.

Northeast Ohio pools get two heavy debris seasons. In spring it is pollen, maple seeds and oak flowers, often right at opening. In fall it is leaves, especially on wooded lots. Big debris should be caught by the skimmer basket and pump basket long before it reaches the filter. Fine pollen and broken-down leaf matter do reach the filter, and that is where filter type shows.

A DE filter catches that fine material best, which is why it keeps water clear through pollen season, but the same fine layer can load up quickly and push the pressure up. Expect to backwash more often in May and again in October. A large cartridge filter holds more dirt before it needs attention, so it may go longer between cleanings during those weeks, at the cost of less polish. Either way, empty baskets often, run the pump at a higher speed while debris is heavy, and use a cover when the pool is not in use.

Water left in a filter tank in an Ohio winter can freeze and crack it. At closing, the filter is cleaned, drained, and its drain plug and pressure gauge are removed and stored inside. For a DE filter, closing is a good time for the once-a-season full grid cleaning so it starts spring clean. For a cartridge filter, the cartridges come out, get cleaned and are stored dry. Our closing and winterizing service includes the filter.

Sand filters are the third common type. Water passes down through a bed of special filter sand, and you backwash to clean it, much like DE but with no powder to add. The sand lasts for years before it needs replacing. The trade-off is filtration: Pentair puts sand at 20 to 100 microns, the coarsest of the three. Sand is a reasonable, low-fuss choice on some pools, but for the water clarity we want on a new pool, we build with DE or cartridge.

Yes, for the first days and weeks. A freshly filled pool carries dirt from construction, dust from the deck work and whatever was in the fill water. Pentair's DE filter manual notes that new pools carry a large amount of debris and may need daily backwashing until it clears. A cartridge filter will need more frequent hosing in that stretch too.

That is normal and it passes. We run the startup, set the pump schedule and show you how to read the pressure gauge. Write down the clean starting pressure once the filter is fresh. Every cleaning decision after that comes back to how far the needle has climbed from that number.

More than most people think. A filter with more surface area holds more dirt before the pressure climbs, so you clean it less often. It also puts less resistance in the way of the pump, and a variable-speed pump saves the most energy when the system is easy to push water through. When we size equipment, we lean toward a larger filter than the minimum for the pool's volume. It costs a little more once and saves effort and power every week of every season.

Choose DE if you want the clearest water possible, you do not mind a short backwash routine, and you have a sensible place to send backwash water. Choose a cartridge filter if you want the simplest do-it-yourself maintenance, want to avoid backwash water and powder, or have a lot where backwash discharge is awkward.

Every Ohio State Pools fiberglass package includes a Pentair DE filter as standard, alongside a Pentair variable-speed pump, Pentair MicroBrite LED lights and a pool heater. Packages start at $68,400 installed. If you would rather have cartridge filtration, tell us at the design stage and we will spec it instead. Both work well with a variable-speed pump, and a larger filter of either type means less frequent cleaning and lower pump energy.