Hmmm just for clarity are you meaning to say plywood or particle board? Theyre very different things.Inset within 3/4 inch plywood, which is also epoxied.
The bad thing about particle board is once it gets wet and soaked through, its virtually useless. It swells up and is very difficult to dry out so dry rot sets in very quickly, turns into a crumbly, weak mess of a material.
The good thing is your lumber frame is very very stout.
If i had this to do over and still wanted to use particle board i would consider lining the entire inside of the tank in fiberglass, not just the seams. Or use sanded plywood instead with the same treatment youve done. i just dont trust particle board for anything but firewood lol.
But simply adding more layers of epoxy could work well as suggested above. Idk though, epoxy aint cheap and would hate to waste it if you arent confident thats going to address the problem.
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