Wiring advice/help needed (voltage in tank)

[GoFish]

I posted a couple weeks ago about checking voltage in tank water here. I had what i thought was i minor problem, got zapped with my hand in the water, checked with voltage meter got some readings, figured it out..It was a T5 light covered in salt creep and i bypassed the ground prong on the plug. plugged it into proper socket. Lesson learned. I installed a GFCI just after that happened and put a rid-volt in the tank. No more readings. Fast forward to last night. Zapped again . The rid-volt has a crappy suction cup and fell out. Put the grounding probe back in and still felt the zap.Tested the water THIS time on the proper voltmeter setting 0-200v AC (last time i was using 0-20v DC, oops) 54 volts!

Unplugged everything one by one and the voltage dropped bit by bit for every device. Its not one thing but everything?

With everything unplugged i get 2.7 volts (this is literally with NOTHING in the tank plugged into a power source)
with the lights plugged in it goes up to 4.5v
+ skimmer 21.6v
+ heater 32.4v
+ koralia powerhead 40.8v
+ aquaclear filter 54.0v
+ rid-volt and it drops to 4.0v

Theres more to the numbers but too much wiring stuff and i get a headache. Did i install the gfci wrong? ive tried 2 separate powerbars and get the same basic results. Its a super simple tank setup, if someone is good with this stuff and can fix it i'll pay in beer, frags, money, whatever. The fish and corals dont mind but i don't wanna get zapped again

Blah