Everything dies except blue damsel

I measured a peak of 50mV when the leads were 1 inch apart. Is this deadly?

 

Set it to 120 AC, put the ground (black) probe into the GROUND on a wall socket, and the red probe into the tank and measure from there.

~Will.

 

I measured 3 VAC.


As far as more pumps...
Here is the top of the tank showing the amount of agitation. It is a lot. (My blue LED's are temporary fit checked, kind of messy)



Here is the sump. It also has a lot of mixing.

 

Thanks for the input. I will take my water to the LFS and see if they can find any issue. Also I may pick up a UV lamp to support a parasite free environ.

 

I also went ahead and grounded the tank using a coat hanger. It will serve until I can get to the store.

 

Next time, don't acclimate the fish for so long, just temperature acclimate them by sticking the bag in the tank for 15-20 min. Then add a little tank water every 5-10 for another 30 min, then add the fish. Too long of an acclimation can stress the fish out even more. Also, try adding some hardier fish, tangs are not nearly has hardy as other fish, especially the powder brown. I also agree that it could be the vendor of your fish. They may be sick before they even get to you.

 

Okay thanks. Tangs were the most recent I also had, at different times, 4 clownfish, two blennys, and a keyhole angel. I really feel bad about the losses.

 

I've thought about it more and I am a little confused about the grounding of the aquarium. It seems that there is not really any relative voltage in the tank. I only measured .05Vdc. But when compared with the grounding of the house there is more voltage but all that means is there is a floating ground between the house and the fish tank. So I could introduce a shock, to myself, by touching the tank, but the fish in the tank would be unharmed. It is much like a bird on a power line. So the floating ground is not harmful to the fish, then what is harmful? Grounding to "earth" or the house only permits a possible current path if something does short out. It would be worse for me and the fish. I have it on GFCI but still could be an issue.

If the mag pumps act as a transformer that the saltwater can create a relative current from one side of the aquarium to the other, them maybe the fish would be in jeopardy, but I do not think it is possible for the potential to be very high. These are not very strong magnetic motors. If the magnetic field is harmful to the fish then there is little else but to turn off the pumps.

It seems highly speculative to say stray voltages from a floating ground causes fish death and I would like to hear from another who can further this thought.