you dont need to flush your nutes really, this just gets rid of all the healthy things that your plants still need up until the end. You can reduce you ferts up till the last week, then just run water, with about a 200 or 300 ppm. This reduces harshness. Also, the way you cure could be the problem. Dry completely on the stem hanging upside down in a cool dry DARK place until crisp. Remove the bud, put it in a cardboard box (absorbs moisture) for another day. Then put in sealable glass jars. About once a day burp the jar allowing fresh air in. If too much moisture is present. Leave off the lid until it crisps again. Keep doing this until your bud spongey but not wet. It should dry to rolling capacity in about 2 or 3 minute. That is about perfect. The longer you cure it the better and smoother the smoke.