08-12-2003, 02:37 AM
Join Date: Mar 2003
I have read several articles in the Krib discussing the types, calibration, maintainence, etc. of pH probes used with monitors and controllers. Two aspects stand out relating to the accuracy and use of the probes in standard, freshwater aquariums. First, the "ionic strenght" (total dissoved solids, GH) of the water being monitored; and second, the affect that "stray voltage" can have on the pH readings. Although minimun GH values were not mentioned, it was clear that very soft water may not have a sufficient ionic strenght to give enough current to accurately read a voltage relating to the pH. My GH is <1, if not zero within the test accuracy. So, it sounds that using a probe to monitor the pH in my tank may not work. If this is true, have minimum GH values been determined for the use of probes in very soft water? Does adding CaCO3 [limestone) raise the GH effectively over a short time period, i.e. 1-2 weeks? I only have one GH test kit [Tetra) so I can't verify that the GH is accurate but it seems to make sense. In southeast Louisiana the ground water primarily perculates through sand [silica) and clays. I cross checked the KH between two test kits and the result was repeatable.
The "stray voltage" affect apparently comes from the various electrical connections associated with an aquarium....lights, filters, etc. Is it recommended that a "ground" probe be used when using a pH probe?
I found it interesting that the various authors of these articles, George Booth and others, use an inexpensive pH test kit to check the "accuracy" of their pH probe...go figure.