Pool Pumps & Filters: Sand vs Cartridge vs D.E.

The easiest way to understand your equipment is to follow one litre of water around the system.

The trip around the system

1. Into the skimmer and main drain. Water is pulled off the surface through the skimmer, where a basket catches leaves and bugs, and from the bottom through the main drain if your pool has one.

2. Into the pump. Before the impeller, the pump has its own strainer basket, which is the second line of defence against debris. The impeller spins and pushes the water onward under pressure. If this basket fills, or air leaks in around the lid, flow drops for everything that comes after it.

3. Through the filter. This is where the fine stuff comes out: dust, pollen, algae cells and the haze that makes water look dull. As the filter traps more, the pressure gauge on top creeps up. That reading is your simplest health check.

4. Through the heater, chlorinator or salt cell, if you have them. Most of these need a minimum flow to work, which is one reason a dirty filter can cause “heater problems.”

5. Back to the pool through the return jets, which also set the surface circulation that pushes debris toward the skimmer.

For keeping all of this in shape week to week, see pool pump and filter maintenance explained. The rest of this page is about choosing a filter.

Sand vs cartridge vs D.E.

Which one should you choose?

Sand suits owners who want the simplest routine. Turn the valve, backwash and you’re done. The trade-off is slightly less polished water and more water down the drain each time.

Cartridge filters give clearer water and save water, which is useful in the dry weeks of a Toronto summer when you’re topping up the pool anyway. Cleaning them is a messier job, and having a spare set to swap in makes it far less of a chore.

D.E. gives the best clarity, but it takes the most work and needs care with the powder itself. Check your municipality’s rules on where backwash water can be discharged, since D.E. and chlorinated water shouldn’t go into storm drains.

Before switching filter types on an existing pool, check the size and flow match your pump. A filter that’s too small for the pump clogs quickly. One that’s much too large is just money spent.

When the pressure tells you something

• Climbing roughly 8–10 psi above the clean reading: time to backwash or clean.
• High right after cleaning: worn sand, a cartridge past its life, or a blockage on the return side.
• Unusually low: a flow problem before the filter, such as a full basket, an air leak or a closed valve.

Questions we get asked

How often should filter sand be changed?

Every several years for most residential pools. Over time the grains round off and stop trapping fine particles.

Can you service my filter?

Yes. See our pool filter service page for sand changes, cartridge cleaning and D.E. service in Toronto.

Is a bigger pump better?

Not necessarily. A pump that’s too strong for the plumbing and filter wastes power and can strain the system. See energy-efficient pool pumps.