One of the, if not THE most ignored components in balancing our pool water is probably the pool water’s temperature. Why? Well, it’s because we naturally assume that temperature only affects the water’s comfort level and does nothing for our overall chemical levels. Partly, this is true because temperature actually does nothing for chemical levels, but it directly affects the pool’s LSI, which in turn is the aggregate “balance” or how corrosive or scale-formative our pool water is.

What is LSI or the Langelier Saturation Index?

LSI in a nutshell is basically an aggregate computation of different factors in our pool that determines how corrosive or how scale-forming our pool water is. LSI is determined by five variables namely pH, calcium hardness, total alkalinity, total dissolved solids (TDS), and pool water temperature.

If you want to learn more about LSI, check out this comprehensive guide on the Langelier Saturation Index.

I cover my pool during winter, why should I be worried?

While pool covers pretty much protect the rest of the variables varying during the off-season, it can’t prevent your pool water temperature from considerably dropping, which in turn will typically drop your LSI levels (if not pre-empted) to the corrosive levels. When we first take off the covers when spring rolls by and we see calcium deposits at the bottom of our pool we immediately think “scale!” and we would be wrong because it’s a lot more complicated than just scale. Let’s see what happens, shall we? But first, we have to assume that we have perfect pool chemical balance before the pool.

  • You cover the pool, assuming that everything is in perfect balance, we expect nothing to go wrong over the winter.
  • The temperature drops, turning the LSI from perfectly balanced to perfectly aggressive (corrosive)
  • The corrosive water eats the calcium from your pool surfaces, trying to balance out your LSI level.
  • The LSI levels even out since the calcium hardness levels have increased from the water eating away at your pool surfaces.
  • The temperature increases, this time turning your LSI levels towards the other direction and causing the excess calcium in the water to re-calcify all over your pool.
  • You uncover your pool, and you think, SCALE! BUT I perfectly balanced my pool before closing it!

How to counter this phenomenon?

The way we suggest countering this phenomenon is the way we usually tell all of our readers how to go about maintaining their pools and that is, slow and steady wins the race! Remember, the temperature doesn’t drop from warm to freezing cold overnight! So as the temperature gradually drops, include the water’s temperature every time you test the water. For every 10F drop in water temperature, adjust your calcium hardness levels up by the corresponding amount to balance out the LSI. We’re talking about an increase of 50ppm for every drop in temperature.

The same goes for when the water is warming up, it doesn’t go from freezing cold to warm just overnight. Once the temperature starts to go up, slowly decrease your calcium hardness levels (or dilute the water) by 50ppm for every 10F increase then once summer is here then you shouldn’t have a problem with corrosion and winter dust.

I don’t have a pool cover, what do I do?

Well, this actually simplifies things a little bit because we’ll assume that since you don’t have a pool cover, you’ll be keeping an eye on your pool water over the off-season much more intently than those with pool covers. A way we can do this is to raise our calcium hardness levels to the maximum recommended levels (400ppm) and just account for the future drop in temperature. And if we keep to a standard maintenance routine level during the winter, we can expect the calcium hardness levels to go down over the winter from water loss due to cleaning and dilution from rain.

Are winterization kits worth it?

Sold out

There’s no real easy answer to that as different online shops and different vendors have different things included with their winterization kits. But if we’re talking about Mr Pool Man’s winterization kit that includes a phosphate remover, an algaecide, and some clarifier, then we can honestly say that this is absolutely worth it. The reason why we say this (and not just because of favoritism) is because this kit contains all of the essentials that will keep your pool water crystal-clear when spring rolls in. This kit also allows us more time to focus on changing variables like water temperature so that we not only have clear water once we reopen but a pool that’s free from corrosion and scaling as well!


Dealing with winter pool balancing entails a change in mindset. During regular pool maintenance, we prioritize the safety of the pool users as we focus on how comfortable the water is and the sanitiser levels. During winter months, we shift focus from sanitiser-centric balancing to more LSI-centric balancing to protect our pool surfaces from corrosion and scaling. Of course, we still have to worry about algae growth but not by much. The cold water and low temperature actually inhibits algae growth so as long as we keep our chlorine levels around the 1ppm - 2ppm levels then we should be preventing algae blooms once the water temperature starts rising.

Need help in calculating your pool's LSI? Check out our comprehensive guide on LSI here.


Check out this free LSI Calculator from AquaCheck

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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