How do I know when my pool filter cartridge needs to be replaced?

The pressure gauge is the main clue: after cleaning, note the clean pressure, and replace the cartridge when it climbs 8-10 psi above that. Visually, look for tears, frayed ends, or stiff, brittle pleats. If your pool stays cloudy after a fresh chemical balance and clean cartridge, it’s not filtering properly. Don’t wait until you’re running the pump longer—a blown cartridge risks debris and pump damage, and a new one costs less than a new pump.