Most two part epoxies will work, as long as you mix them completely. Separately, the epoxy components can break down in the water and may harm your animals. As long as they are mixed properly, it all sticks together with no problems. Once mixed, you can apply it underwater as well.
I haven't seen any epoxies containing mildew/mold resistant chemicals (found in bathroom silicones) but never use a product containing them in your aquarium.