I test that little iv had api master test kits expire and they have a self life of years , it’s 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 don’t need to tell me there’s just little indicators that let you know , if I test my tank it’s because I already know there’s a problem and the test is just to tell me how much water needs to be replaced to solve the problem