I’m seeing at least a 2 volt increase in the tank per heater. Have 2 heaters in the sump and one in tank (for emergency). The two in the sump are Aquatop 300W heaters where the controller is on a cord, no control in the water. Seems odd that all 3 heaters would be causing this, can there be some interaction between them and something else? Anyone seen this with this heater?