MH's are great for the planted tank. They are very good at illuminating the lower levels of a deep tank.
Look for 6500K or 10000K bulbs for better color.
The draw back is that they are a bit awkward for general illumination purposes. If you plan to keep your tank lit for longer than the 10 or so hours of your plants' grow period, the MH's are overkill.
If you can put the MH's on a timer and supplant them with a flourecsent fixture for sunrise and sunset, you've got it licked.
I've been using MH's in my planted tank for years and recommend them. I have a reef fixture, MH/ flourescent combo, over my 135.
I haven't found a source for 6500k's outside of the aquarium suppliers so the price, as you can imagine, is pretty high.
I've found that there's a difference in the color of 6500k's from different manufacturers. The "Superbrite" Day bulb from Hamilton is too green, IMO, but is much less expensive than Coralife's lamp, which has great color.
You'll need to change out MH's every 12 to 18 mos. They don't look like they've lost light but they have. I think, too, that the light spectrum shifts over time making them less effective.
If I had to do it all over again would I buy the same fixture? I know that power compacs light the lower tank well, are cheaper, and have great color. It would be close.
Later.
