yeah, a good majority of halogen energy is wasted as heat. Like stated above, a lot of Amano's set ups use MH and if you find a ADA dealer they will sometimes sell ADA MH bulbs. Be prepared to shell out for the bulbs though, they're very expensive.
if i have a 400w metal halide that i got from a hydroponics store... is it strong enough for a low-tech/light plant set up in a 8x2x20"? i was thinking just have this one light in the middle of the tank...
You've have one ridiculously bright spot with a bunch of algae. How big is the light? With a low-light/tech setup, you don't want to go with much over 1.5 wpg (depending on the type of source. T5, PC, MH, etc.). Once you get above there you have to deal with algae.