Winter Pool Water Chemistry

Winter Pool Chemical Levels
by Mark Garcia October 1, 2013

Winter Pool Chemical Levels

icy poolWinter pool water balance - is it different than summer? Yes, for the following reasons:

1. Cold water, below 60, is harder for algae to grow.

2. Winter air is cleaner, as cold dense air sinks.

3. Less sun reduces chemical consumption.

4. Less swimmer wastes to deal with.

5. Pool is possibly cleaned less often.


Here's how to maintain winter pool chemistry, for pools still open and operating in the south, and for pools that are covered and closed.


For pools in the lower half of the country, in warmer areas where freeze is uncommon, pools are unused but still need to be maintained. Most pool owners reduce the pump operation time, reduce their sanitizer level, and generally reduce their pool care altogether. Makes sense, no one's using it, right? 

Chlorine can be reduced during winter, but should not be allowed to drop to zero. Use enough tablets and a low setting on the chlorinator to keep a reading of 0.5 - 1.0 ppm. If you are using a mineral sanitizer like Nature2, you can allow this to drop further.

pH in the winter pool can be allowed to rise as high as 7.6, a little higher than I like to run it during the summer, but keep it in range. Very high or low pH during winter can be harsh on your pool finishes. To help buffer your pH, keep the Alkalinity normal, in the 80-120 ppm range.

Calcium hardness in the winter pool is important, to protect your pool surfaces and finishes. Too low, and it can attack pool plaster during winter. Too high, and you can develop calcium nodules, sharp crystalline deposits. Maintain a 180 ppm minimum.

Cyanuric Acid. Just like during summer, a level of conditioner, or stabilizer is recommended, in the range of 30-50 ppm, to reduce UV degradation of your chlorine. The winter sun is not as strong as a summer sun, so you can operate in the lower end of the range.


For pools in the upper half of the country, you have or soon will close the pool, and cover it for winter. Be sure to balance the pool water before closing it, and adding your winter pool chemicals.

Solid Covered Pools: For those pools covered by a good solid cover (one that won't rip, or has small holes), you can count on a stable water balance during the winter. If your pool water becomes contaminated (by rips or holes), you should remove and repair the pool cover, clean the pool and balance the water chemistry. However, if your pool cover is sturdy and you have it solidly installed with enough water bags, you *should* open up to a clean and clear pool.

Mesh Covered Pools: Because a mesh pool cover (or a solid safety cover with drain panels) allows rain water and snow melt to enter the pool water, winter water balance is always changing.

Mesh covered pools should have their pool water chemistry checked several times during the winter. If possible, check it at least monthly by pulling back a corner of the cover, and running the full battery of water balance tests.

In areas with acid rain, dust, pollution, pollen or pools with overhanging trees, water balance changing particulates are constantly filling a mesh covered pool. These can create algae growth, produce staining, or give you poor water quality for days or weeks after opening the pool. Ahh-Some Winter Pool Clarifier

Because of the constant contaminants being added to a mesh covered pool, use extra chemicals to help neutralize and coagulate them. Two of my favorite products to use in addition to my winter chemicals are Ahh-Some winter clarifier, and Pool Magic, to help control this problem with some mesh covered pools. If your pool opens not just dark and hazy, but full of green algae, try some Pool Magic + Phos-Free.


Thanks for Reading!

Mark Garcia