how often to change 20000k 400w mh?

[yuriy]

how often to change 20000k 400w mh if I use 400w blue line ballast,did any body use 400w20000k bulbs from hellolights.com ? who sells cheap 400w 10000k mh bulbs ?It is a lot of questions aaaa?

[cbonito]

I use the XM20k bulbs from hellolights, and they are great.

I am getting good growth and coloration under this bulb.
The price is also right. All of my SPS have developed more intense pigments since adding this to the center of my tank.