pH probes...

[Robert Chady <aquatic-plants at chady_org>]

A little while ago my probe indicated my pH seemed to be going down,
but KH was staying the same and my plants were not bubbling like they
had been.  I used a couple different test kits and they all showed that
my pH was in the 7.2ish range, while my pH probe was recording it at 6.6.
So, I re-re-recalibrated it and it at least got a bit closer to where
it seems it should be.  However, after a few days the recorded pH is
off quite a bit again.

The sad part is this pH probe is only a few months old now. :(  I tried
letting it soak for an hour in pH 4.0 solution, but that doesn't seem to
have helped.  

So, my question (finally), does anyone have any pH probes they can
recommend that last longer?  I am using the probe with an aquacontroller
II if that makes a difference.

Robert Chady
Chippewa Falls, WI