ORP probe issues????

[JohnK]

So I, among others jumped on the O3 bandwagon after Calfo's presentation.

I wanted to be safe, I got 2 ORP controllers and connnected them one after the other so as to have redundancy to avoid O3 overdosing risks.

PROBLEM,

I got one controller with probe from a respected BRS member, and another controller without probe from another respected BRS member. I got a new "lab grade" probe for the controller W/O a probe.

Now after a month or two, I have two controllers that read/work exactly the same but the probes give way different readings. I have switched the probes back and forth repeatedly and the readings are within a +/- range of 2-5 mV for each probe seperately on either controller.
BUT.
The new "lab grade" probe consistently reads about 50mV lower than the "barely used" (Milwake) probe.

What the heck does this mean? Is one probe bad and if so which one? Neither shows any visable signs of damage.

Anyone have any ideas what might be going on here?

thanks
jk

 

[smcnally]

Did you calibrate each probe seperately?

 

[clamm]

do you have any calibration fluid, if not last time I bought 10 packs so msg me before the meeting.

 

[JohnK]

Yes and no.

The monitors I have are sandpoint and milwake, neither has a calibration adjustment (lame, I guess you check with cal solution then you know your aproximate error?).

I have 230 mV calibration solution and if I remember correctly I got smilarly funky readings, but consistently lower on the one probe vs the other. I'm in the process of testing that now to see what exact numbers I'm getting.

 

[JohnK]

Ok, so as I changed out a couple of old VHO bulbs I spilled my calibration solution so I guess I'll post again in a few days when I get some more

 

[RichConley]

I've been reading a lot about that, and it seems that as they get dirty, they creap up a little, and start reading higher. Have you cleaned the probes? I've heard soaking in vinegar or alchohol will work, although I'd think vinegar would be the more reef safe.

 

[JohnK]

Cleaning did make a difference for the better, I'll post again when I get new cal solution.

jk