What is wrong with my seedling?

Well, here's two things I know I'm doing wrong, you can tell me if you that that its the cause.

1) I'm just using straight tap water w/o evaporating it for a good day or two like I should.

2) I'm using about a 30-70 earthworm castings-soil mix right now. I'm guessing that even earthworm castings can give a plant nute burn but I really didn't think that was possible until now.

I have the little guy sitting under a 2600 lumen cfl cool light bulb. About an inch away but not to the point that its burning up I don't think. Well, my little guy looks like it almost has purple on its leaves but upon closer inspection its actually more like black or brown spots. My first grow was similar to this except I used to distilled water and maybe a little less earthworm castings in the initial mix. Would my "mistakes" that I've made with this grow cause these spots on my plant? Would you suggest anything to try to save it or should I use my last seed and hope for the best?