Most Marin pools don't need a full winterization. You keep the water in, keep the pump running, and keep the chemistry balanced through the rainy months. What changes is the schedule: shorter pump runs, a plan for frost nights, and cleanup after every big storm. Closing a pool the way people do back East causes more trouble here than it prevents.
Why shouldn't you drain or close a Marin pool?
The full shutdown (blown-out lines, antifreeze, a tarp, no pump) exists for places where the ground freezes for weeks. Marin winters don't do that. They bring rain instead, and rain is the reason to leave the water in.
Winter storms push groundwater up around the shell. A full pool weighs enough to hold its ground. An empty one can crack, or lift out of the soil, when that water presses from below. If a repair ever requires draining, schedule it for the dry months.
A pool that sits still under a tarp until May also tends to come back green. Clearing a swamp in spring takes more time and chemicals than steady winter upkeep.
How long should the pump run in winter?
Shorter than in summer, and every day. Cold water slows algae growth, and the sun burns off less chlorine, so the water needs less circulation to stay clear. It still needs enough to turn over, push chlorine through the whole pool, and pull leaves into the skimmer.
If you have a variable-speed pump, run it longer at a low speed rather than a short blast at high speed. You move the same water for less power. Don't switch the pump off for the season.
Do Marin pools need freeze protection?
Inland pools do. Novato, San Rafael, and the Ross Valley towns of San Anselmo and Fairfax see frost on clear, still winter nights. Fog-belt pools in Sausalito and Tiburon see it less, but a cold snap reaches them too.
Moving water resists freezing. The damage comes from water sitting in exposed above-ground pipes, valves, and the pump housing. Most automation systems include a freeze-protection setting that starts the pump when the air temperature drops near freezing. Three things to check before the first cold night:
- Freeze protection is turned on in your controller.
- The air sensor reads a believable temperature.
- The equipment has power. Freeze protection can't run if a storm trips the breaker or knocks out PG&E service overnight.
After an outage on a cold night, walk out to the equipment pad and confirm the pump restarted.
What do winter storms do to the water?
Rain dilutes everything you balanced. Alkalinity, calcium, and chlorine all drop as fresh water pours in, and the water level climbs. Once the level rises above the skimmer opening, the skimmer stops pulling leaves off the surface and they sink.
Wind brings the debris. Redwood needles, oak leaves, and eucalyptus bark pack skimmer and pump baskets fast, and a clogged basket starves the pump of water. After a big atmospheric river, work through this order:
- Empty the skimmer and pump baskets.
- Check the water level and lower it if it sits above the skimmer.
- Test and rebalance the chemistry.
- Check filter pressure and clean or backwash if it has climbed.
A mesh safety cover keeps most of that debris out of the water. We covered the tradeoffs in Do You Really Need a Pool Cover in Marin?
Salt systems and heaters in the cold
Many salt chlorine generators shut off chlorine production when the water drops below a set temperature. The control panel may show a cold-water warning, and the pool goes without new chlorine unless someone adds it by hand. Check your model's manual for its cutoff and plan on liquid chlorine through the coldest weeks.
If you don't swim in winter, turn the heater off at the controller so it doesn't fire on a chilly morning. Mice and rats like to nest inside idle heaters, so have someone look inside the cabinet before you light it up again in spring.
The short winter list
- Keep the water in the pool.
- Run the pump daily on a shorter schedule.
- Turn on freeze protection and check it after outages.
- Clear baskets and test the water after every storm.
- Add chlorine by hand if your salt cell stops in the cold.
Our weekly service runs all winter, Monday through Friday, and covers every item on that list. Call us at (415) 562-8143 or send a request.