Noticed the same thing with finger shocks. Added a grounding probe & no longer feel the shocks, leading me to believe there was in fact some stray voltage. Ordered a voltage meter & will be keeping tabs on it moving forwardMy tank is about 6 months old. Recently started noticing when I put my hand in my sump, if I have any cuts on my hands, get a very sharp pain in the cut. Much sharper pain than that of saltwater in a cut. I'm suspecting I'm having stray voltage into my tank. I just ordered a ground probe and will be installing a gfci outlet. Also will be checking with a volt meter.
What makes me even more suspicious that I do have stray voltage is a believe I've had issues with the bacteria imbalances in my tank. For example I was trying out Aquachar. Alot of people say that it'll float for the first while and after about a week or so it'll populate with bacteria and begin to sink down. I have mine in a mesh bag and weighed down with some rubble rock so it stays submerged. After 6 weeks it would still be able to float which tells me it isn't populating with bacteria. I talked to several people who use this product and all were baffled. Which now leads me to Beleive that possibly stray voltage in my tank is affecting my beneficial bacteria populations