We just swapped chips in our 80's to Halo color from the metal halide. Seelite chips were I believe $18 per 40 ($36) per light and $25 per 100 ($50)per light. We actually put Arrow LED chips in ours as the were less expensive and a buddy is running Arrow LED...12- 100 watters on his rig and the are super LED lights. As far as the difference from Halo to HPS I really can't help out with. Most of the water we shoot in stained pretty good and the Metal halide was just to white to do any good. Swapping the chips though is a pretty easy task.