These Flex 4 Test Strips are designed specifically for use with the Taylor Xpress Flex® water system. The strips test for phosphate levels. Test strips have long been the go-to testing method for pool and spa owners and for a good reason. The dry chemistries used in these strips are as reliable as those in Taylor’s liquid reagents, and testing couldn’t be easier. Just dip into a collected sample and read. No technical know-how is required. Within seconds you’ll have a good picture of the condition of the water and whether or not any adjustments are necessary.