SEASHELLS IN BETTA TANK?

I have a few seashells and a conch shell that I want to put in a tank I will soon be getting. I am not too worried about the old organism's bacteria in the shell because it has been old and dry for well over a decade. What I want to know is will old salt hurt the fish? I heard I could bleach the shells then allow them to dry outside and the bleach will evaporate. Basically, what can I do to put them in the tank?