Make sure you switch the adapter to the correct mode, pH or ORP.
pH formula for the Arduino sketch: PHLevel = (0.0178 * (PHprobe) - 1.889); This assumes 25 degree C.
ORP formula for the Arduino sketch: mV = ((2.5 - ORPprobe / 200) / 1.037)* 1000;
Words of Caution from Phidgets
The pH Adapter Board should be used to measure solutions that are 'electrically quiet'. Measuring pH in electrically noisy environments such as tanks with mixing pumps, and even other measuring devices is not recommended.
I have had some noise interference from the hot tub jets when the filter cycle is running, but overall the Phidgets adapter has worked well in the hot tub environment.