I think one of my tomato plants has blossom end rot?

Question

I read it may be from a calcium deficiency my first question is would it effect only 1 plant? Only 1 is like this. Could it be the epsom salt I used ? I used a bit in the soil when I first transplanted my seedlings I also use guano gro an organic fertilizer and rabbit manure. my 3rd question is if it is a calcium problem can I use the same calcium on the plant that I feed to my reptiles? should I apply it to the surrounding soil or to the foliage? would it hurt to try this just to see if I get results? I haven't tested my soil all of my other veggies are doing very good and I have very minimal bug problems. (I have an organic garden so there are a few pests but not many) thanks for any pointers! sorry this is so drawn out I'm a first timer so any advice is appreciated.