I was going to reply to you Ryan, but Steve and Danny covered the answer well!

If you look at the spectrum plot of a 10K compared to a 20K, the real difference between the two is that 10K has a high "blue" output as well as fairly high output in other ranges, while a 20K has even higher "blue" output and barely any output in the rest of the spectrum. So there is no need to supplement light in the blue range as 10K has good output in the blue spectrum. Unless you want your tank to look bluer.