Winter Water Chemistry Basics

Winter Water Temperature

If you live in a climate where pool winterization is required, this article will help you.

Most pool service technicians don't come back until the season is over. This practice is a missed opportunity. Winterizing pools is a skill that can be utilized by both parties involved in the industry. It can be a lot of work and it can be done well.


"Just Following Industry Standards"

What is the chemistry of the water after pool winterization? Usually, this process involves treating the water with chemicals that are used in the industry.

We use industry standard ranges to manage water chemistry. The goal is to maximize chlorine efficacy while keeping the water clear and safe.

When it comes to winterizing a pool, do not just consider the cover or the water clarity. The priority should be to maintain a balanced water balance, which includes chlorination and sanitation.


Water Temperature and Sanitization

As the water temperature rises, so does the demand for sanitizer. Also, the more organisms are active in warmer temperatures, the faster their reactions occur.

Winter is a great time to keep a pool algae-free. The temperature difference between summer and winter is the main reason why.

As the water temperature drops, enzymes begin to slow down and go dormant. This is the case for most chemicals.

The temperature of the water should also be taken into consideration when preparing for pool winterization. If you're planning on adding calcium or bicarb to your pool's LSI, make sure that this step is performed weeks before the water is warm enough to close. Also, make sure that the mix is full of no undissolved material.


Phosphate removal, enzymes, and sequestering works better in warmer water

A phosphate treatment is typically done a week or two before the pool winterization. This is because it gives the reaction time to complete and clean up the precipitate.


Pool winterization can wait

In some cases, October can bring nice, warm weather. This can be even in the Northeast and Midwest.

  • Allows for a longer season of pool use and enjoyment
  • Lower closing temperatures (less chemicals required to adjust for the upcoming winter)
  • Increased revenue for pool service companies

If the water is cold enough, but not too cold, then wait a few more weeks. This will help the customer and the service company as it will keep the pool warm during winter.


Pool Crystals

In colder places, calcium crystals form on the cement surfaces commonly used for flooring. They are extremely difficult to form and are caused by low LSI. Usually, these crystals are treated with acid to prevent further damage.

We have been able to prevent many types of crystals from causing this issue. We can even cure it in the spring.

  1. Balance the LSI of the water
  2. Purge the pool with 32oz of SC-1000 per 10,000 gallons of water. SC-1000's pH does not lower the LSI, it actually helps raise it, while gently breaking down calcite into solution.
  3. Continue using SC-1000 weekly and maintaining LSI balanced water (-0.30 to 0.00, so the LSI value is yellow on the Orenda App calculator) until the crystals are gone.


Simplified practices

If your pool has crystals of calcium, it means that its water is consuming too much calcium. We recommend adding 400ppm calcium to give it some grace.



  • If possible, extend the season into October. It gives the swimmers more time to use and less time to close. It's also beneficial for the service company's bottom line.
  • Cold water is very important when it comes to pool winterization. It slows the production of sanitizer and lowers the LSI.
  • Remove phosphates at least a week before pool winterization so you have time to come back and vacuum, and clean the filter.
  • Purge with CV-600 when the water is still above 65ºF. It is very helpful to do a deep clean of the inside of the pipes before clearing the lines and lowering the water level.
  • Not over-chlorinate during the last week of the season. It's important to remember that the demand for sanitizer is only going to decrease as the temperature drops.
  • If you winterize pools, we suggest adding 400 ppm calcium. Use the OrendaLSI calculator to manage it.



This post was originally published on Orendatech Blog


If you have any other questions about pool and spa products please do let us know - we are here to help!


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