Not much credence is given to pool store testing around here. While you would think that a "professional" would be the best, unfortunately in most cases it is quite the opposite. Between employees who blindly trust the word of chemical sales representatives and high school kids working in the pool store for the summer you end up with poor results from their testing. But, what can you do?? We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. Order a TF100 and I also have the SpeedStir and Sample Sizer. They speed testing and accuracy.