Here is the best explanation of flushing I've ever read, and what I attempt to do in my grows. It also gives a good explanation as to why your product can have that chemical taste and not burn cleanly. Plus it also blows the lid off the organic vs inorganic argument. Flushing is the last of the highlighted links near the top of the page.
Great link. The flushing info really puts things in perspective I am going to have to read the rest of through a few times... biology and chemistry always gave me headaches!