Winter calcium (calcite) crystals that form in swimming pools are an ever-increasing problem for both pool owners and pool maintenance professionals. Their sudden appearance is unexpected, often with no explanation, with little known about how we can prevent them. Calcite crystals are a major issue across the Northeast region of the country, especially in newly plastered swimming pools. New maintenance protocols are being implemented among pool owners in the Hamptons to combat the problem.

The maintenance professionals at Tortorella have provided some further insight on the ever-increasing problem of calcite crystals, why they could potentially appear, and how to treat them in the future.

What are Calcium (Calcite) Crystals?

Calcium crystals are different from the more common winter dust and winter scale phenomena which are caused by low LSI (Langelier Saturation Index) and high pH during winterization. These more well-known pool ailments occur as the water warms and calcium is drawn out of the water, depositing dust or scale-type calcium in/on top and around the water and nearby surfaces. Unlike other mineral deposits such as scale or dust that can be found in water, calcium crystals form on the cement beneath the surface of the water. This is because the water itself extracts calcium from the plaster, allowing for their growth underwater. In comparison to the calcium scale that forms due to high pH and/or hard water, calcium nodules caused by plaster delamination (bond failure), and cracks, the appearance and form of these entities are quite different. While there are a few different formation types (see our sister article on What are the 4 Types of Calcite Calcium Crystal Deposits) generally speaking they range from short to sharp and to long and spike-like crystals. Remember, they will only be found growing from cement surfaces and in tile grout- never directly on tiles or other surfaces such as plastic, glass, metal, etc.

What Causes Calcium (Calcite) Crystals to form?

There is great debate among industry professionals as to how these little crystals form. Here are several potential explanations that have been proposed;

  • The formation could result from ‘aggressive water’ which occurs when pools have not been properly winterized and adjusted for the soon-to-be cold temperatures- producing a very low LSI.
  • Due to the “aggressive water” this could turn into an undergoing issue due to the dissolving of the plaster from the pool lining- causing calcium crystals to start growing on the surface.
  • In winter, temperatures in the Northeastern states drop significantly and stagnant water pools call for more etching damages. These damages can lead to an increase in potential growth of calcium crystals on top of the cement- creating low LSI,
  • In newer pools, the culprit has been attributed to a combination of poor plaster workmanship with aggressive water. With concerns that the plaster compounds “bleed” into the pool water, increasing the pH, alkalinity, and calcium level.

How to treat/prevent calcium crystals in my pool?

In the short term, certain acid products can remove the crystals, however, we prefer a more environmentally-friendly agent that binds to the metals and minerals which helps dissolve the calcium crystals back into solution – removing them from your walls. A professional pool maintenance technician will also work to adjust your pH and alkalinity to balance your LSI . A good balance helps to bring everything back under control!

As for a long-term solution, make sure your pool LSI is balanced. Failure of balance will cause the water to crave more calcium leading to the creation of crystals. We can not stress the importance of a proper winterization strategy – ensuring all environmental factors: weather, the chemical makeup, and the age of your pool. Remember, colder temperatures yield a lower LSI.


Either way, there is a lot more about the crystals that we have yet to learn. That’s why our pool maintenance technicians are staying adaptive and focusing on staying one step ahead of this ever-increasing problem. If you have any questions or need advice on how to manage this problem please don’t hesitate to contact us!