You get induced voltages, I thought I had stray voltage and with everything u plugged apart from the light that doesnt even touch the tank I was getting 36v. I wouldn't say it's a voltage issue.Sorry...i tried a newer extension cord and these are my findings:
All equipment off 5.8v
Only heater on 12v
Only powerhead on 12v
Only return on 35v
With everything on besides the return it hovers around 20, with all equipment on it's showing 42.