Problem: Scale
Cause: Calcium carbonate (scale) is not very soluble in water. As the calcium, pH, or carbonate level rises in the water, calcium carbonate will form and can precipitate. As this happens, it adheres to surfaces and equipment. Temperature also plays a role in this process, as calcium is more soluble in cold water, which also tends to be more corrosive.
For this reason, a little more calcium should be added to the water when closing the pool. This will adjust the saturation index slightly higher so, as the temperature drops, the water does not fall too far into the corrosive range. However, it is a delicate balancing act, as too much can cause scale to form as the water becomes warmer.
In areas where the source water already contains a high calcium level, this needs to be factored in each year during the pool opening process.
Treatment: If the pool was partially drained and the fill water is not high in calcium, the level will naturally dilute as the water is topped up before opening the pool. If the fill water is high in calcium, a scale inhibitor product should be added when the pool is being opened. It is important to ensure the product that is used is not only suitable for treating or inhibiting scale, but also is compatible with the sanitizer system being employed. For example, citric acid is not a scale inhibitor or preventer and is not compatible with a salt chlorinating sanitation system. The active ingredient can usually be found by looking at the safety data sheet (SDS).
Prevention: First and foremost, the pool water should be properly balanced upon closing the pool. A scale and corrosion preventer can also be added as part of the closing routine. In high calcium areas, a scale inhibitor product should be added on a monthly basis, again, ensuring the product is appropriate for the sanitizing system being used.
Special considerations for saltwater Swimming pools
Always follow the manufacturers’ instructions for the salt chlorine generator’s cell start-up process. If the cell was not cleaned when the pool was closed, then the opening process offers a great opportunity to clean it. The cell is prone to scale due to the high pH inside the unit. High pH is normal for this process and is a byproduct of chlorine generation. However, pool owners should be advised to do what they can to mitigate scale formation on the cell plates.
As scale builds on the cell plates, it reduces their ability to make adequate contact with the water, which impedes the production of chlorine. Cells must be cleaned periodically (on an annual basis) to ensure any scale is removed. When doing this, it is important that a scale inhibitor product appropriate for saltwater pools is used, even if the calcium in the water is not too high.
As saltwater pools are essentially chlorine-based sanitizers, all of the water quality problems discussed in this article could potentially be encountered. That said, the treatment process is the same—algaecide, shocking/oxidation, clarifiers, and pump run time. Saltwater pools may require some supplemental chlorine product upon opening until the generator is producing chlorine at the desired level. It is advisable to continue using an appropriate scale inhibitor product throughout the season regardless of the calcium level.
What is the takeaway? It is important to close the pool properly in the fall. Any problems that exist during this time will not go away over the course of the off-season. However, if these problems are encountered come spring, there are remedies to prevent them from happening again. With the proper treatment procedures and a little patience, pool downtime can be kept to a minimum.
Karen Rigsby is the business support manager, R&D for BioLab, a KIK Custom Products Company. She has been involved with the recreational side of water treatment since 2001, focusing on education, problem resolution, and new product development. She started her career in the water treatment industry at BioLab as an analytical chemist in the research and development group. Prior to recreational water, Rigsby was employed by the Georgia Bureau of Investigation as a forensic chemist. Rigsby received her bachelor of science in chemistry from Georgia Tech and is a member of the Association of Pool & Spa Professionals (APSP) Recreational Water Quality Committee and a National Swimming Pool Foundation (NSPF) certified instructor.
