First, cdness did you see my tank. Lol a stupid penny wiped out my whole tank in days!!! Second and back on point there can't be stray voltage from a wand. Sorry but I can't take the loose terms. Now you could have cause a stray "current" if you had a better ground then the one on the wand and that is my guess. Current kills people, not voltage. Stray "voltage" is not a problem. When you were building your wand could you have messed up the ground? If so you were basically electrocuting your animals if you had a ground probe or a bad pump giving the current a path other than up the wand. do you have a ground probe in your tank?
No matter the case glad everything is getting better. Either you produced to much chlorine, freed copper into the water or electrocuted everything.