I think it depends on the species of clam as well as the species of acropora. Also whether you want to keep the color of the acropora. I think intense lighting is required to keep blue acroporas blue. I personally would never keep a SPS & clam dominated tank without MH.
actually i'm not intending to keep them. I was just wondering. just to know more. beside, it's hard to get acro here. over here sps come in cheap and can be see all over the marine shop (well there are not much marine shop here) but acro. hak~ I haven't only seen one of them~
and when I talk about acro i mean to keep the special coloured species in thier colour. I heard that they usually got brown when keep in tank. so they demand more light to be in red or blue?