How much stray voltage will cause issues?

[IamJoHo]

How much voltage would you say could start to cause issues? Tested and found that I had around 12 volts in the tank then started to remove power from things in the tank and found that when I unplugged the reactor pump the voltage dropped to 4-5 volts. Would either of those levels cause any issues?

 

[Jay Hemdal]

How much voltage would you say could start to cause issues? Tested and found that I had around 12 volts in the tank then started to remove power from things in the tank and found that when I unplugged the reactor pump the voltage dropped to 4-5 volts. Would either of those levels cause any issues?

What kind of issues are you worried about? My only concern is for human safety. What you measured may simply have been induced voltage from the electromagnet in the pump. All the other things stray voltage has been accused of causing, like HLLE are unproven as to actual causation.
Jay

 

[ca1ore]

Correlation is not causation. PE is reduced and you measure 12 volts ….. must be the reason. Fish died and you measured 12 volts ….. must be the reason. No bigger red herring in the hobby than stray voltage. I have literally never, in 35 years of reefing, been able to reliably link small levels of stray voltage to any specific problem. Most of the time it's induced voltage anyhow, so turning off a pump may well reduce or eliminate the voltage even when there is nothing wrong with it.

What you DO want to keep an eye on is any kind of break in submerged wires. Use and maintain a grounding probe. On my system, all devices with submerged wires (of which there aren't that many) are on a GFCI, so if there is any problem the circuit will cut. I also keep the connection end of my submersible heaters out of the water.