DWC grow, plants not drinking 7-8 weeks intolower

So a few weeks ago I ran out of complete NPK nute and was too lazy to get to the store for a few weeks, the plants went through a severe nitrogen deficiency which led to nute lock. I then got off my ass and rushed to the store to get some more. After putting it in the res they still were not drinking. So I emptied it out last week and flushed with pure water. Ater this weekend they were drinking water almost at the same rate they had before. So I put some nutes and molasses back in the res and now they stopped drinking? could they just need more time with pure water or what? I am using a 400 HPS,floranova nutes, and Grandmas molasses. I am thinking that it could be the molasses. Has anyone ever used this kind before? thnx