I am new to TFP, came upon the site searching the internet for reliable pool water tests. Dissatisfied with using pool supplies company tests and recommended chemicals for 15 years. 19,000 gal pool exposed to sunlight all day at up to 117F in the summer and down to 59F in the winter (freezing temps seldom and short term at night). Little rain but lots of wind blowing dust. Challenges: hard water, septic tank (no public sewer).