Electrical question

[spreerider]

your sink should be grounded if its metal and it its not it wont matter as it wont conduct anyways.

A GFCI works by measuring the current entering (hot) and leaving (the identified conductor commenly called neutral) you can have a ground fault and not have a gfci trip under the right circumstances but a solid connected ground is not necessary for a GFCI to trip as the current in a fault without solid ground could still make it to ground via a person or object.
i use a GFCI but no ground probe.
BTW most aquarium products are not grounded they are double insulated you can tell because none of them have a 3rd prong on the cord, the only thing that usually is grounded is the light as some require a proper ground to startup lights, and often have exposed metal on the fixture that needs to be grounded as per CEC and CUL.