A GFCI will trip if a device say a hair dryer or any (dry) electronic device falls into water. They are installed on most SW system power supplies in a mistaken belief that they will trip in the event of say a malfunctioning device, they usually will not, this is where I seriously recommend a good grade surge protector, you will spend a lot on it too but there is no sense in $10,000 tank depending on a $1.99 surge protector. Also if you install your GFCI under your tank, inside the stand it could trip due to excessive moisture build up and render your tank without power.