Lochaber, I do go to dendroboard and they definitely have some real expert advice -- so good advice. Mixing sand with epoxy might look good. And, im2smart, thank you for the link -- those are both well crafted backdrop -- I'll test Drylok, for sure.
My man concern is, obviously, that I kill my fish, plants or inverts. Inverts are especially sensitive as we all know, and, once I get a tank built, I want 100% confidence that if I change the inhabitants the new residents won't croak.
I suppose I could do a Mengele and buy some drylok and put a blob in a tank with a couple of shrimp and see if they survive.
There was a mudskipper tank that may have used drylok or something similar that I'm sure you've seen -- pretty inspirational.
Thank you for the feedback!