We use fiberglass reenforced mortar. Its what thay hand make shower floors from around here. My build tank we are lining with ceramic tile(wood build). I think its more to personal preferance. But cure time needs to be a few weeks at least. I would be leary on regular concrete mixes due to such high amounts of calcium and other chems that seep as it cures. But lots of people have success. I wanted to use hydraulic as well but an ornery old dude im very close friends told me not to. And hell show me the good way to do it lmao. He suggested the fibreglass reenforced because it is more like an epoxy. We shall see... but its good to see what other options i have.