Hi

I have some problems with pH measurements. I have a GHL system that controls two different water systems. The line-up is PB6-PB6-EXPBOX(1)-PH6-EXPBOX(2)-PB5-PB5-PROFILUX 3.1T. PB6-PB6-EXPBOX(1) control system 1 and EXPBOX(2)-PB%-PB% control system number 2. Each EXPBOX use the internal pH, redox and temp card plus 1 extension pH card. (EXPBOX(2) has also air temp/humidity extension card and 1 temp/humidity probe. The system 1 works perfectly and has done that for app 5 months. System 2 is started 1 week ago. Both are freshwater. All 4 pH probes was calibrated yesterday – using the same pH 7 and 4 fresh pH 9 calibration fluids. After calibration all 4 shows the same if I put all at the same spot in system 1 – they show the same value. There is a titanium heather working as a grounded probe in system 1.
The problems start when I put EXPBOX(2):s electrodes in system 2. The value start vary up to 1 pH unit and values was not relevant. After adding a titanium heather also in system 2 (just use it as a ground probe) – the readings became more relevant but has a funny pattern with changes of up to 1 pH unit in periods. For the probe attached to the expansion box internal pH card is the changes linked to illuminate channel 1. If that channel is on – the pH reading drops 0.5- 1 unit! And this is not linked to any attaching to a power bar outlet – just only linked to if illuminate channel 1 is on or off!!!!.
Now - I do not use Ill 1 for my lights – I use Ill 3 instead and that channel has not the same effect to my pH readings. I also use ill channel 2 without any problems. Now when I do not use Illumination channel 1 – this probe works.
However the second pH electrode (linked to extension the card of EXPBOX(2)) still can vary with up to 1 pH unit. Looks like the changes is connected to something like the other electrode but I have not found out what is the problem. I think that the first problem was different potentials in the systems – but the link to illumination channel 1 and the last example – I can´t understand. Can someone help me?

I use firmaware 6.14

Sincerely Lasse