The only thing I can recommend is when you decide to get more fish, add only one and see how it does. If your water parameters are fine, (being 0 nitrates, nitrites and ammonia) and your Ph is a stable 8.2
But is your alk really 200?
The alkalinity of a saltwater tank should be around 2.5 to 3.5 meq/l. I'm not sure what kind of test kit you have, could you let us know what you are using?
Too, you should have zero nitrates. How often do you do a water change and how much?