Keith wrote:
I've got a tiny hairline crack in an integral fiberglass water tank
that I need to repair. So far, folks have suggested epoxy, JB weld,
polyester resin, etc., but no concensus has appeared. Any suggestions?
Any reason not to use aquarium type silicone caulk? Anything else I
haven't thought of? TIA.

This is how I would do it, YMMV.

You don't indicate where the crack is, but assume you have access and
can drain tank as req'd.

Sand all around the crack with a right angle sander equipped with either
24 or 36 grit disk so that you have at least a 2"-3" sanded surface
around the crack.

Make sure the area is really scuffed up and is clean by sweeping up the
debris before proceeding.

Laminate about 3-4 layers of 6" wide boat tape with some good laminating
epoxy over the area making sure all surfaces are sealed.

Allow to cure at least 72 hours.

Lew