What is TDS?
TDS - Total Dissolved Solids - represents the "volume of mineral solids, salt and metals dissolved in water". It is measured in PPM (parts per million) or mg/l.
Soluble materials are almost everything you put in your pool or spa, such as disinfectants, specialty chemicals (clarifiers, algaecides) and balancing chemicals (pH, stabilizers, alkalinity)...
When there are too many, these materials can cause oxidation of certain materials or interfere with the effectiveness of treatments.
By measuring water soluble material, the effectiveness of your disinfectant and other related factors, ICO can alert you when your TDS is too high and recommend actions to correct the problem.
How to calibrate your ICO
This video tutorial explains why and how to calibrate your ICO.