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[APD] Re: pH probe problem with Dennerle controller.

Hi Chris,
I have some experience with this area. I currently use three pH controllers 
with my three planted tanks.

Let's get the "I hope I am not insulting your intelligence" question out of 
the way. Your controller has 2 point calibration, meaning one adjustment dial 
for pH 7 solution and one for pH 4 or 10 solution, either a small dial or 
something you use a screwdriver to adjust. Make sure you are using the proper 
adjustment point with the right solution.

If you are, then your probe is probably bad. I have never been able to 
refresh a probe, personally. For me, when they fail to hold a calibration or cannot 
hold one at all, then it is time to get a new probe.

Sometimes the probes are bad when you buy the controller. It has happened to 
me twice. The probe tip is usually the weak link in the controller setup 
itself anyways. Some controller manufacturers used to ship the probes with these 
rigid clear plastic covers that didn't hold the solution they are shipped in 
well. They leaked and the probe tip dries out and fails. Most probes now have 
flexible tip covers that hold the shipping solution well. In both cases the 
manufacturer cheerfully replaced the probe, so no big deal. Just because you bought 
it second hand, it is still factory sealed and should work when opened. 

If there is a US Dennerle office, you might try direct contact with them 
about getting a free replacement. They will do this sometimes. I had a bad probe 
shipped with a Milwaukee Instruments SMS 122 controller I bought thru a 
reseller, and I handled it directly with Milwaukee. Great customer service from those 

If you have to buy one, I would recommend the least expensive Broadley-James 
replacement probe, available thru Drs. Smith and Foster. It is the same Ag-Cl 
type found in all the planted tank grade controllers out there and it is only 
about $34.99 last time I bought one. Looks just like the probe you get with 
the American Marine pH Controller or Monitor.

Finally, IME, the single biggest thing you can do to keep the probe working 
thru its normal life is to_never_ let it dry out. That will kill a probe faster 
than anything else I've seen. 

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