I test that little iv had api master test kits expire and they have a self life of years , itās all about your tank in my opinion you can notice things after a certain amount of time within a set up same as I know when my dogs are not well they donāt need to tell me thereās just little indicators that let you know , if I test my tank itās because I already know thereās a problem and the test is just to tell me how much water needs to be replaced to solve the problem