Simply put, no. These are brackish water species. Your CK will not tolerate brackish conditions. I'd suggest returning it to your lfs if you cannot keep it in brackish conditions.
It may not be the correct way to keep one but I do have one that was purchased from a 100% FW tank and it is and has been living in a 100% FW tank with my gold clown and my silver arrow among others. No signs of stress or slime issues on the fish as of yet. It always eats and seems healthy. Eats only bloodworms.
what cool looking fish could live with a ck in my tank? (that's not to much) even p.senegalus is $40 for a 3 incher or $15 for a 1 incher, and I dont think a 1 incher would be ok with any size CK