You need to ground the hood and tank.
The third prong on a power plug does that. Do a search on the internet for a grounding probe or something like that and you can find some better information and a product. If it is shocking you there is a power leak, you should trace all of your power lines and see if there is something that is exposed to water. (Possibly a power head thats no longer completely sealed, or a wire that has a slit.)
Do some searches on grounding and you should get the info that you need.