I was too late to the game I tested nitrates at 5 and phosphates said 0.03 I got a second opinion and their hanna showed 0.01 then he re took the test and showed zero so my kit was faulty near the end of use by date so now I dose p04 and a little roids occasionally and either nitrates or acro power. Does any one know how long after dosing phosphates I should test? As if I dose then test in 24 hrs the results are the same as the day before. I just dont know what is using it at presentDid you happen to test for nutrients as it declined? I have a love/hate relationship with the accuracy of test kits and mainly just use them to establish trends. Even the all mighty Hanna ULR doesn't give me warm fuzzies. I had a serious event where my PO4 was at 0.02 on test kits and things were going south fast. I always read posts where people say as long as there is a trace you're good...any level showing on a test kit means you have enough. Time and time again I am reminded by how quickly stuff goes south when po4 is low. I dose PO4 whenever my hanna ULR reads 0.02 or less and stuff looks great.