Possibly starting first ever small FOWLR SW tank and looking for info

[Magma]

The koralia nano PH would a for a 6gal tank its small I have one in my sump to keep the water moving in there.

Grounding probe is not needed, get a GFCI plug or GFCI powerbar and you will be fine, the grounding probe will take any stray voltage you have in the tank and give it a path to ground which is great but IMO it hides the fact theres a problem, at least if a GFCI trips you know you have a problem. I just checked my tanks with my meter and one tank had 0.04V showing and the other had 0.02V all used equipment expect my power heads so personally for me with a combine total between my two 40gal tanks of 0.06V im not worried at all.