There are several things that could be causing your problems, and heat from the ballast could be a part of it, but there's mostly likely other causes that need to be rooted out. For instance, sawdust makes soil acidic, and you need to have a way to test the pH of your water and soil. Even if it's just pH test kits for aquariums, which are available practically anywhere, it's important to know (and regulate) your pH.

Along with that, fill out this form as best as you possibly can. It's hard to guess what all might be causing the problem when we don't know hardly any details about the grow.