Personally I have always been most concerned with scenario #1.
Scenario 1. Hot line to water via submerged equipment. This is when a submerged piece of equipment like a powerhead, heater or UV lamp fails and the hot line of the power supply gets in contact with the water:
d) Ground Probe Installed and GFCI installed: As soon as the short circuit is established the GFCI will trip shutting down whatever equipment is connected giving you a physical indication there is a short and something bad for you to fix immediately. This is the safest situation for the aquarist but has the downside that if you are away from the tank for a long time the lack of operating vital equipment may put your critters at risk.
So under this scenario the safest for the aquarist is to use both a GFCI and a ground probe.
It has already proven itself to me, when yrs ago when the Stealth heaters were being recalled, with some going off in tanks like pipe bombs, with enough force to blow ends of tanks out. I had a crack in one of my Stealth heaters that couldn't be seen by the naked eye from outside of the tank - but thanks to the combo of a GFCI/Grounding Probe the defect tripped the circuit off, and potentially saved me a disaster. I simply isolated one piece of equipment at a time by unplugging until I found the faulty heater, and after a very close inspection found the crack. Disaster averted.
As far as increasing the sensitivity of the GFCI, you have to be careful as you can potentially end up with what is known as "nuisance trips". A small power surge from a storm etc could potentially cause it to trip. Not a huge thing if you check your tank daily, but not great if you are away for any length of time.
Scenario 1. Hot line to water via submerged equipment. This is when a submerged piece of equipment like a powerhead, heater or UV lamp fails and the hot line of the power supply gets in contact with the water:
d) Ground Probe Installed and GFCI installed: As soon as the short circuit is established the GFCI will trip shutting down whatever equipment is connected giving you a physical indication there is a short and something bad for you to fix immediately. This is the safest situation for the aquarist but has the downside that if you are away from the tank for a long time the lack of operating vital equipment may put your critters at risk.
So under this scenario the safest for the aquarist is to use both a GFCI and a ground probe.
It has already proven itself to me, when yrs ago when the Stealth heaters were being recalled, with some going off in tanks like pipe bombs, with enough force to blow ends of tanks out. I had a crack in one of my Stealth heaters that couldn't be seen by the naked eye from outside of the tank - but thanks to the combo of a GFCI/Grounding Probe the defect tripped the circuit off, and potentially saved me a disaster. I simply isolated one piece of equipment at a time by unplugging until I found the faulty heater, and after a very close inspection found the crack. Disaster averted.
As far as increasing the sensitivity of the GFCI, you have to be careful as you can potentially end up with what is known as "nuisance trips". A small power surge from a storm etc could potentially cause it to trip. Not a huge thing if you check your tank daily, but not great if you are away for any length of time.
