Phil,
I do not have the calibration procedure for the Aquadyne pH controller, It looks like a good piece of equipment I wish I had one.
As far as accuracies go, every pH electronic device must be calibrated, and a typical calibration involves something like this;
Enter calibration mode.
Place pH probe in buffer solution of a known value ( let's say you put probe in 7.00 pH packet). This is called "standardize".
Let it stabalize for a few minutes.
Read what the display is saying, and if not exactly reading 7.00 then enter 7.00 on the keypad and enter into the unit.
Rinse the pH probe in distilled water.
Place probe in the other known pH buffer solution, the pH buffer packet of 10.00 ( called "slope" ).
Read what it is now displaying, and let it stabalize for a period or time.
If not reading exactly 10.00, then enter 10.00 on keypad and enter into unit.
Rinse probe and go back to 7.00 packet again to check, then rinse again and place it in 10.00 again to check. Sometimes you are asked to enter the temperature of the buffers at some point of the calibration procedure. This is a typical calibration method.
The pH probe puts out a millivolt signal when placed in a liquid. Typically in a buffer solution of 7.00 neutral pH, it will put out approximately 00.00 millivolts ( which the controllers displays as 7.00 ) At a pH of say 4.00 the probe will put out +177 millivolts, and in a buffer of 10 it will put out -177 millivolts. As the pH electrode ( probe ) gets old, these millivolt values will begin to drift on you, thus the need for frequent calibration checks. All you are doing when you calibrate the probe is "offsetting" this natural drift of the probe and correcting the display to read the offset. Think of the ph probe as a battery ... and as it gets older, it gets weaker. So you must calibrate the probe to the controller often to insure a correct reading.
Also be aware that it is not uncommon for the pH in our tanks to fluctuate a good deal throughout a 24 hour period. Depending on how mature your tank is, the amount of buffering capacity, number of fish/inverts and development of algae, it is not unusual for the pH to drop to around 7.9 in the early morning and get as high as 8.4 in the late evening ( assuming you are normally around 8.20 pH ).
ORP stands for Oxidation Reduction Potential, is measured in millivolts as well, and is sometimes helpful for people adding ozone to improve their water quality.
My advise to you would be to just follow the calibration instructions for your Aquadyne equipment to the letter, let the probe stabalize in between buffer solutions, don't rush the calibration procedure, and check your probe in the known buffer solutions often, especially when you noticed any changes from what you consider "normal" for you tank.
Sorry for the lengthy reply here .... but I do find pH/orp to be rather interesting measurements.
Good luck my friend
Broomer
