I could not believe the lfs
said that, that light will support corals and clams. Well maybe I can. That light for clams for that tall of a tank will run you probably $500 so hopefully you got a super discount!! lol. I have never heard of that side light, I guess it makes sense but if you buy a Metal Halide fixture for the top you should be ok with just that and nothing for the side. Do you want your corals facing up or sideways? Probably up, so I would go with a fixture on the top.
3 Gallon Betta, 14 Gallon BioCube Planted, 29 Gallon Community, 29 Gallon Parrot Cichlid/Pleco
46 Bowfront Reef Tank, 3 Cats, 1 Choc. Lab