It's not like that with t5 bulbs. I've never seen a 20k bulb per say in t5's. They are named something like aquablue which is equal to a 12k bulb or 75/25 which is around 14k, but I've never seen a 20k t5 bulb. I would go with an aquablue, 2 blue +'s and maybe a fiji purple or true actinic...