I went straight from 12K to 20K, and form 400w x 3 to 250w x 3 and didnt notice too much, corals definantly didnt open up the same for a couple days, but nothing major happened and nothing perished. Keep in mind with my switch not only did the spectrum change but the entire PAR changed as well. I think youd be more than fine making the jump to 20K IMO.