I am new to the forum. I have a three year old indoor Endless pool. Although I have been balancing water for three years, I realized (after reading on this site) there is still a lot I don't know. Recently, I was told I need to start measuring TDS and SI. I was told to purchase a digital TDS device. I have done some reading (I will check out the pool school here) and have found out that TDS is a pandora's box, probably for all issues regarding water balancing. Since I use bleach for my Chlorine source and Sodium Bisulfate for my acid source, I would assume my TDS is mostly sodium. I have read that TDS has very little impact on the calculation of SI. I have also read that there are two major groups that do and don't recommend draining and refilling pools based solely on the TDS. Anyway, I will do more reading.