Yeah. It happened again. One of our vats is leaking. :( Checked the date of the re-seal on the side - 5 years ago. :/ Seems no matter what we use, wood or concrete...they leak every 5 years. Or at least one did.
Been there, done that. At least right now the farm is reasonably empty! I think I may have a nervous breakdown moving EVERYTHING again...of course it is one that is full. :/ Moral support, please? Maybe liquor? LOL!
Have you thought about painting the bottom of the vats, inside and out, with fiberglass hull paint for boats? The stuff will waterproof just about anything. It would require draining though. Also Apoxie Fix it is a product that will set under water. It's marine safe and is used by the atlanta aquarium to fix stuff in their displays. (I used the sculpt for rock work but it has to be used dry). You may be able to use Fix It to patch any future holes.
Well, when something like this leaks...there is no "hole" per se. Most of the time you can't even find where it is/was...the walls don't stay clean of coralline and so on, so unless it was at the very bottom it would be very hard to tell. Even if it WAS at the very bottom it may be impossible to tell...because a fine crack in it could slowly leak with 650 gallons of pressure. To even give yourself a chance at finding it, you would have to empty the whole thing anyway...and once you have done that you may as well seal the whole thing again.
We use marine epoxy...we have some fiberglass we can mix in...but we didn't like how rough it was with the fiberglass in there when we used it last time. :/