Do yourself and your plants a favor and use a commercial flusher.

You are so late in flower you may want to think of 1/2 strength and only feed every other water. It will take them time to perk up and you don't have that much time left. If you are going to use boosters make sure you cut back on other minerals or you will over feed the others too. Some strains can take it at the end but not all of them.