at the depth of the 75 gallon tanks,i think less than 20 inches,you might not see a difference between mh and t5 accept the t5 will not give the rippling effect.if you do it,i'd love to see which side is brighter.
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55 gallon reef with 4x54 watt t5,29 gallon sump,red monti cap,1blue echinophyllia,trumpet,red lobo,2 toadstools 1purple and 1neon,gsp,xenia and yellow xenia,red ,many mushrooms,2 giant frilly shrooms,cabbage coral,yellow polyps,many zoos,1 orange and one neon green nepthia,duncans,cladiella | 
Mixing lighting (T5 & MH) 
