Phoenix 14K makes the green color appear more vivid than XM 20K. I like both 14K and 20K. The only thing I miss is the intense neon blue color that 20K brought out on the bodies of my blue eye cardinals. However, the blue mushroom appeared more purple under 20K and it did not really intensify the blue and purple colors much on my blue acroporas. 20K is initially very blue, but after a few months of use, the blue spectrum of XM 20K mellows out. Then the only difference I noticed was the afforementioned effect on the blue eye cardinals. When I replaced my XM 20K (actually double end bulbs are called XDE) with Phoenix 14K, I noticed the brightness of the 14K light and the vivid yellow and green. Hamilton 20K (over 8Ball's old tank) looked the same as XM 20K to me.
Tomoko