How long does the Sutro Test Cartridge last? April 30, 2020 03:45 Updated The Sutro cartridge has 90 tests available, and since it tests 3 times per day- will last for roughly a month. Related articles How much does a Sutro cost? How often does the Sutro test? What chemical parameters does Sutro test for? Why does the Sutro Test Cartridge rattle when I shake it? How does the Sutro take a reading? Comments 0 comments Please sign in to leave a comment.