If you have a saltwater pool, you know it isn't filled with ocean water. In fact, the sanitizing agent in your pool is the same hypochlorous acid (HClO) you find in chlorine pools, so winterizing a saltwater pool isn't much different from winterizing a conventional chlorine pool. A saltwater pool typically has a generator that produces chlorine from ordinary salt, and it's important to protect it from the elements when shutting down the pool for the winter. It's just as important to protect the filtration system and the pool itself.
Cool Weather Can Make the Pool Water More Acidic
A saltwater pool has the same filtration system as a regular pool, and the water should have about the same chemical balance. The difference between the two types of pools is the electrolytic chlorine generator (ECG), which is an electrolysis cell on the pressure side of the filtration system in the saltwater pool. The ECG generates hypochlorous acid, eliminating the need to add chlorine to the water. With the onset of cool weather, this generator begins to function slightly differently, and that may affect the pH of the pool water. That's why it's important to balance the the pool chemicals shortly before turning off the generator and covering the pool.
Most ECGs have sensors that measure the conductivity of the water and alert the person maintaining the pool to add salt when needed. As the weather cools, the conductivity of the water decreases, and the sensors may call for more salt than necessary. This can raise the pH and make the water corrosive, and the results won't be apparent until spring, when the pool is uncovered.
Test the Salt Levels Manually
Because the salt sensors become less reliable as the weather cools, it's important to test the salt levels with testing strips, which are not affected by temperature. If the salt levels are higher than they need to be, hold off on adding salt until the levels return to normal -- which is ideally around 3,200 ppm.
Balance the Chemicals
Pay special attention to pH, which should be between 7.2 and 7.8, total alkalinity, which should be between 80 and 120 ppm and calcium hardness, which should be between 200 and 400 ppm.
Add an Anti-Staining Agent
Minerals in the water tend to settle on the sides and bottom of the pool during the winter. To prevent this, add a scale and stain sequestrant designed for saltwater pools. Turn the pump on, and circulate the agent through the water for at least eight hours prior to closing the pool.
If the pool has a mesh cover or a solid cover with a drain panel, it's a good idea to add slow-acting enzymes to the water. They will digest any oily residue that gets into the water during the winter.
Winterize the ECG, and Plug the Pool
Unplug the chlorine generator, and then consult the manufacturer's instructions for the proper way to winterize it. Some manufacturers recommend draining all the water, while others say you can leave a mixture of water and nontoxic antifreeze in the unit. If the generator is easy to remove, the best strategy is to unhook it and take it indoors for the winter.
Cover the Pool
Place two or more air pillows on the surface of the water to support the pool cover, and then place the cover on the pool and fasten it down. It's a good idea to additionally cover the cover with 1 to 2 inches of water to prevent it from flapping in the wind.