Question about flatworms and Flatworm Exit

[dc4]

So, the last few days my elegance coral was looking about 1/2 closed and I didnt really think anything of it but last night when I got home from work, I noticed a few brown spots on it. I did a quick search which brought me to believe that they were flatworms. I did a fresh water dip and saw about 10-15 little brown things floating in the water. When I put the elegance back into the tank, it stayed shriveled which I was expecting and is about 1/3 fully open this morning but with no more brown spots.

Now to my question, I do not notice any other corals with any spots and no noticable spots on the live rock but due to the elegance having flatworms on it, would it mean that there are flatworms hiding everywhere? If so, would it be safe to use Flatworm Exit as a procautionary measure just to prevent an outbreak?