what has been your feeding schedule for ur plants....basically you should flush....two weeks before ur gonna harvest do as rusty said and flush two or three gallons of phd water through your pots....i usally do this by adding one gallon and then wait twenty minutes before flushing the others through...i do this so the water from the first gallon has time to dissolve some of the salts so they r flushed out when you add the rest...after that make sure to let it dry out..pretty much just go back to ur normal water schedule but using only phd water till the chop...one other thing..make sure to let them dry out before u chop..helps the drying process