Since I use a small amount of salt in my African tanks, I have gotten shocked. I used to have salt water tanks and I got shocked even more often. Something was wrong and trying to kill me.
Let’s figure this out. Unplug everything. Use a multimeter, set it to AC voltage, put the black probe in the ground hole of the wall socket and put the red probe in the water. Use this as a reference ground voltage. If you see voltage greater than one volt you have a more serious home wiring issue and I’d call and electrician. For complete gibberish about why one volt is acceptable read Ground Loops @ MIT.
Now you have to figure out which appliance is creating the shock. Plug in one appliance at a time repeating the test. Anything greater than our reference voltage indicates a problem. It could be more than one appliance, so test them all. I’ve had submersible pumps, heaters, and lights all become faulty. But more often it was due to a bad drip loop.
A drip loop should be used for every appliance in a fish tank, especially a tank with salt in it. The cord will proceed down from the tank and a loop is formed at the lowest point, then the cord proceeds upward into the socket. This prevents water from dripping down the cord and into the socket. But salt can still creep back UP the cord. Just clean the cord with a clean wet rag and then dry it off and that should solve that. If not, replace the appliance or take it to your workshop and pull out the tools and good luck.
I just installed a GFI which will break the circuit if it detects a ground fault. It will definitely happen if you get shocked, but it might also happen for other reasons even when you are not in the room. My Africans are pretty darn forgiving and I walk by my tanks a few times a day so I’ll notice if the lights are not turning on and figure out what’s wrong fairly quickly. But if you have a reef tank I recommend a power fail alarm- you can even get them that SMS or email you. Probably cheaper than replacing the stock of a reef tank many times over.
Good luck and don’t die.