Southern California pools often stay filled year-round. Opening still needs a careful first week: cover, water line, chemistry, and a pump that actually turns over the pool.
Before the cover comes off
Sweep leaves and standing water off the cover so debris does not dump into the pool. Check the water line from outside: if it sat below the skimmer all winter, the pump may have run dry. In San Gabriel Valley the ground rarely freezes, but a cover that sat tight for months can still hide algae, a low water line, or a clogged skimmer basket.
Fill, reconnect, then test
Bring the water back to mid-skimmer. Reconnect the pump, filter, and heater unions you loosened in winter. Open the skimmer and return valves slowly so you do not pull air. Test free chlorine, combined chlorine, pH, total alkalinity, calcium hardness, and cyanuric acid (stabilizer). Public-health guidance for treated pools generally keeps free chlorine near 1–3 ppm and pH between 7.2 and 7.8. Shock only after you know those numbers — dumping chlorine into water that is already high in cyanuric acid or low in pH wastes product and can irritate skin.
The first 24 hours
Run the pump around the clock until the water is clear and the filter pressure settles. Brush walls and steps so algae cannot sit in the shade line. Empty the pump basket twice if the cover left a lot of debris. If the water stays cloudy after a proper shock and overnight circulation, the filter — not more chlorine — is usually the next step.