I have used 3M 5200 many times on bait tanks and many other things.
Its great stuff...
We constantly run bait tank with full water change every 15 min. and it is new clean ocean water.
I would only recommend using it on the outside of the temp pond you are talking about (basically a horse trough)
You need to drain and dry the tank very well & give at least 24 hrs to dry before refilling.
5200 is a pretty bullet proof sealant
You probably could get away with using inside also (but wouldn't recommend it)
Good Luck
RookieKoiGuy Grow out Form