It was my first grow and I had problems throughout. so its probably not fair of me to blame the Mars for the airy buds. No doubt others will get far better results than me. Still, I'm going to convert the mars to cobs as per groumouse's guide on youtube.
What cobs are you getting?
I just finished a full cycle with a mars II 900 ( 385 w meausered at wall), see my comments above. They're decent value in relation to similar fixtures, but nobody should be recommending them over pre-built diy-style COB fixtures. They're similar cost but are some of the best lights available anywhere compared to the Mars which will be easily out performed by a HPS of similar draw.