Though listed under "Miscellaneous" don't get the idea that these aren't important! I would never run a reef system without them! Folks, we use a ton of submersed electrical equipment in this hobby. When they go bad most often they will emit stray electricity before failing completely. The most common item to fail ... heaters, especially typical glass/tube type heaters. If you don't have a ground probe on your system & you put your hand in the tank, YOU become the fastest source to ground for that electricity!! Certainly stray electricity at the very least will irritate your livestock but if enough watts are there it can kill them... & YOU!
A ground probe gives you a positive electrical ground for your reef system. The wet end tip is made of pure titanium & provides excellent electrical contact with the water. A long lasting product that is non-corrosive in both fresh and saltwater. Just plug into any grounded outlet and place the titanium end into either the tank water or sump water. I recommend anywhere under the water in the sump. It's that easy!
For more information about stray electricity, see my Self Help article: "A Shocking Problem"