I took out the old doors and associated harware. Got the new doors and
ready to install.

My question is..........

Is there a cetain kind of caulk to use? Everyone I looked at said "not
to be used below the water-line in showers or aquariums". Home Depot
or Lowes don't carry "aquarium" caulk.

Will any of the silicone caulk work?

You don't have to be in the aquarium business to answer. :-)

Hank