Got myself a HANNA colorimeter to test my P04. I was using an elos kit but it was always just clear. After testing with the colorimeter I get a reading of 0.01 Its very easy to use and IMO worht the money, for the kits with a case and reagents its $250 but Ive spent that much over the years in P04 kits anyway. No more looking down through tubes second guessing myself.