I use Salifert and Elos, and test three times each to confirm a new kits accuracy and then test once with each kit after that, but I only test monthly on average. I have had 2 bad Salifert kits over the years, I have not had a bad Elos kit yet. I also have found I make mistakes while titrating on a regular basis and can only combat my apparent carelessness with repetition. I guess I'm not as careful as I used to be. Of course it doesn't help that my son loves to stand next to me and go 12,19,42,8 . . . as I'm counting drops