Debateable. I DO NOT use GFCI outlets. It is against electrical code to install a GFCI outlet on any life support appliances.
Then again it is against code to not use a GFI on an outlet within X feet of a water source, for good reason. The reason you can't use a GFI on a life support device is that there is always the possibility of it tripping, and turning of the life support device. In a fish/reef tank, the GFI
is the life support device, preventing you from electrocuting yourself on your tank inhabitants.
I don?t think it is debatable, but rather basic electrical safety when mixing water and electricity. As GFI have been known to eventually go bad or trip for no apparent reason, I would recommend using at least two GFIs, and splitting your pumps, power heads and heater between the two. That way, if one trips, you will still have water circulation and heat until you can reset the switch.
For those that do not know, a GFI or GFCI (Ground fault interrupt / ground fault circuit interrupt) protects against stray electrical current. Electricity runs through a circuit from Hot to Neutral, usually out of the outlet (hot), into a device, out the device and back into the outlet (neutral). If there is a difference in current between the hot and neutral plug., i.e. when electrical current is deviated from the circuit, either through your tank or through you, the GFI trips turning off the current.
GFI are very easily wired into existing outlets, and cost about $10 a piece.