So I have an electronic pH monitor and it reads 8.x in all 3 tanks I have when lights are off. In one tank though, when the lights go on it shows the pH at 2.5. Lights go off and the reading goes back to 8.x. I figure it is maybe some stray voltage, but I can't measure any with my multimeter. Strangely in that tank, when the lights are on, the pH still reads 8.x when measured in the sump. Any thoughts?