These high quality Tablets are for use only with a photometer. They test for PH in your pool and there are 100 in the pack. All our Tablets have at least 5 years expiry date from the day of purchase. Confused about your hot tub water chemistry?? Our guides answer the most Frequently Asked Questions! Why do I need to test my hot tub / spa / swimming pool water chlorine levels ? Why do I need to test my hot tub / spa / swimming pool water pH levels ?