PH Controller and EI
I started EI about two weeks ago and have noticed something that may or may not be related to the new chemicals I am putting in my tank.
My PH probes have been acting a little crazy lately! About one week into EI my first probe failed. At first I thought it was simply a worn out probe and now am not so sure. When I installed the new one yesterday it calibrated and contolled my CO2 normally (i checked it a dozen times during the day) and this morning it showed a ph of 6.14. It will no longer calibrate. This is exactly what happened to the last probe. Prior to this, I have had excellant results after changing a probe.
I use an automatic dosing pump dosing KNO3, KH2PO4 and K2SO4 in one solution (all analytical grade dry powders mixed in RO water) and Flourish Iron in another. I dose hourly 24x7 the K solutions and 1 times daily 11 ml of Fe to achieve the targets on Wet's calculator.
I was dosing about 3 inches from the probe and noticed a PH shift during dosing of about .5 ph. Before I installed the new probe I moved the K dose to the other side of the tank just in case. Now it is about 1 meter from the probe and I did not notice a PH shift during dosing. Fe is still about 3" from the probe.
My question (finally) has anyone had problems with coating or quickly depleting a probe using these chemicals? To me it makes no sense but I look to the forum for your experience before I pony up for the only thing left ( new electronics). I have two more new probes but hesitate to throw them in the tank until I understand this better.
I am using a Weipro PH control that has gotten mixed reviews on the forums. It is not a meter I would put in a lab but from my experience it works ok for controlling CO2 in my tanks. From what I can tell, the PH probe is a single junction with temperature compensation.
When the probe fails, the set point adjusts itself to match the step change in the probe (seems strange to me too). This is consistent with what I experienced before EI dosing. Changing the probe and recalibration solved the problem in the past. I verify/ calibrate religously monthly.
Any insight or experience would be helpful.