If you are relying on a Hanna Checker, then all bets are off. They tend to be rather poor at returning consistent or accurate results (I have gone through two meters and several hundred reagent packets).
Terri_ann, I read your posts and i question why you are worried about a difference between a .08 and a .05 reading. I mentioned this earlier in this thread that the Hanna checker has a "Precision: ±0.04 ppm (mg/L) ±4% of reading @ 25°C". So to have a difference within that range is normal.
I just didn't think you need to worry so much and check every day.
Just my 2cents.
I hope this doesn't come across in any other way than a question.