I am wondering if you can put shells in a Freshwater Ray tank. I have shells someone sent me to put in my tank from Tarpon Springs Florida. I think I remember you weren't suppose to put shells from the ocean in a freshwater fish tank. Has anybody heard this or am I just getting old and making it up my self. I haven't put them in there yet. I wanted to find out for sure. Don't want to kill my new ray. 