Humic acid is an ingredient in several fertilizers, including the pure blend pro bloom, so you should be fine. I'd use it much lighter than the bottle recommends.
However, its primary function is as a soil conditioner, and I've always just used it when I flush, just a small amount in the final stage of the flush when you also add a small amount of complete grow fert.
So, my instinct is to just use it when you are flushing or trying to correct a lockout or salt tox situation.