Everything except pure water in your pool is a measure of total dissolved solids (TDS).
Whatever enters the pool, either chemical or human, leaves a residue, which increases TDS. It is the ultimate measure of everything combined, including alkalinity, cyanuric acid, chlorides, calcium hardness, bathers’ waste and dirt, etc. It also includes minerals in the city water. The question is should TDS concern pool owners? Advice on this topic varies greatly and for a good reason.
Because heightened TDS levels may cause a substantial, or conversely, no reaction at all, it is probably the most misunderstood factor in pool chemistry. However, it boils down to the main argument— whether or not to drain the pool when TDS reach high levels.
There are two different schools of thought regarding this argument. The first thought is high TDS can cause staining due to the corrosive nature of levels above 1,500 parts per million. Just the possibility of staining justifies draining the pool. Many pool owners opt for this remedy.
However, the other school of thought questions whether draining is even necessary. Experts cannot say for certain whether high TDS will cause any problems, including staining. Why not wait for a better reason to drain? Reasons include high cyanuric levels, which hold strong chlorine readings, or when no chlorine reading registers.
I have cared for pools with TDS higher than 3,000 parts per million for more than 15 years, and have experienced no visible problems. There are other reasons contributing to corrosive issues, such as low pH or low calcium levels. Deciding why a problem exists requires eliminating the obvious causes first.
In my experience, few pool problems materialize when water is routinely backwashed, and not chemically overdosed with additional algaecides, clarifiers and tile cleaners. Using only the correct amounts of muriatic acid to regulate pH and chlorine additions will generally avoid any TDS-related issues.
Remember, TDS is a general indicator of water quality, but really provides little insight about the relationships of the various components and how they interact to cause staining, taste or color problems. Elevated TDS is not a health hazard. So, unless balanced water is causing unexplained problems, I would lean toward not draining the pool until other causes have been ruled out.
If you have pool questions, please call me at (602) 290-8774.