MH's have the nice shimmer effect like in this pic
http://aquariumdesigngroup.com/#mi=2...8&p=3&a=0&at=0
If you don't use CO2 a sump is fine, if you do you will want to try and minimize the amount that can outgas (not sure how to do that but there are threads around here with tips). Worst case you put more CO2 into the water since some will be getting gassed out. CO2 is cheap so its really not a big deal.