Anyone trust their pH Probe? Tricks to calibrating?

[caliman]

Putting my Reef Angel info in my sig was a big motivator to calibrate my pH probe. :hehe:

I had this probe in there for over a year. I calibrated it with the 7.0 and 10.0 solution. It still wouldn't raise above pH 4 so I tossed it as I had a new one.

The new one out of the box seemed pretty accurate (8.3 or so) but I decided to calibrate it. Now it shows my pH in the high 7's. This may well be fairly accurate. In my experience, my nano always has slightly low pH around 8.0.

Is there a trick to calibration? I let the numbers settle for over 5 minutes before hitting 'ok' on my Reef Angel.

But the point is, can I trust these things at all? Are they just a measuring stick?

Kinda frustrated with this.

matt

ph-probe-calibration.jpg (132.32 KiB) Viewed 5093 times

[rimai]

Does it read 7.0 and 10.0 when you dip them in the solution?
If so, I would consider that your pH is correct.

[caliman]

Do you mean after calibration? I will try that. Thanks

How long do you let the numbers settle Roberto?

[lnevo]

It's a measuring stick. The PH may be accurate if you dip it in an isolated cup, but stray voltage in the tank can effect it. I know when my skimmer is on, I drop about .1 pH. I've adjusted my calibration numbers to compensate. What's more enlightening is the trend and seeing your ph remain stable which the RA can do just fine.

The one thing I've learned is if things start going haywire, it's usually the probe and I would doublecheck with a standard test before chasing ghosts.

[caliman]

Thanks for the tips. How did you adjust your calibration numbers to compensate for the .1 drop?

[lnevo]

The arduino map() function is used to map the ph reading that you get to a number between 7.0 and 10.0.

You can see the math in the definition of the map function here: http://arduino.cc/en/reference/map

Code: Select all

long map(long x, long in_min, long in_max, long out_min, long out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

I basically just played with the in_min and in_max numbers adjusting them evenly until I got the pH that I measured by hand.

[caliman]

Wow that can be handy. I'll wait until I get a new salifert pH kit then I will play with this.

Thanks very much.