Can you tell me what drop-type salt test I should use? I have been using the strips that you put in a small vial of water and wait a few minutes to take a reading.

Also, regarding the potential damage to tile/coping etc., I have found only the opposite. I have a Calcium reading on the high side (520 ppm). My overflow from my spa always had a lot of scale. Since the swg has been in operation, the scale has actually been disappearing. Maybe I am just more aware of ph and adding muriatic acid more often.

I do use A LOT of acid--at least 1/2 gallon/week with a 37,000 gallon pool.