Confused by two Ph Meters

I have two Hanna Ph meters that read to the second digit ( x.xx ) that are driving me nuts.

If I put both into a prepared solution, in this case holding solution, they both read exactly the same number. If I put them into aquarium or holding tank water though, they read up to 2.5 full steps apart from each other ( 1 might be 6.62 while the other reads 6.90 ) ??

Could it be the difference with Gh and/or Kh (solution would be higher) that could cause this??

Any ideas??

PS. They both calibrate using 7.01 and 4.01 Hanna solutions

Do you keep the prob end wet all the time? If not then you should put distilled water in the prob cap. What i found with mine was while very accurate in solution. I found if i let it dry out between uses it would get freaky like that. When I'd go to calibrate i would need to let sit in the solution for 15-20min before i calibrated or it would most definitely be off. Keeping the prob end wet did away with that problem.

My solution was a small piece of cotton ball in the prob cap and keep distilled water on the prob all the time.

I keep the little well in the cap filled with storage solution, which over a few days probably becomes more tank water than storage solution, and that may be the problem. Soaked both in storage solution after writing last post and now both meters are reading the same. Guess I'll have to make a point of adding storage solution on a more regular basis - I like your cotton idea though - that's the way they come packaged, although every tip I've ever bought came with the cotton bone dry :p Seems the solution is storage solution lol

BTW - spoke with a Hanna engineer years ago who told me there is a little piece of cloth outside the ball probe and that is what dries out - the meter uses the difference between what the external cloth probe reads as compared to what the prove inside the glass ball reads. I'll be darned if I've ever been able to see anything outside the ball but apparently it's there

If yours are like mine. You should see a little white'ish stick like thing. I believe that is what they were referring to.

A man with one watch always knows the time, a man with two is never sure.

Author unknown...to me.