no, you're not out to lunch at all!! intense lighting will bleach your corals if you don't acclimate them slowly. However if you install those 400w bulbs at 1 foot higher than your 250s then you will get more coverage and eventually you can start lowering your light 1inch at a time over the course of a few weeks. I think what he was getting at is with limited room over your tank, you might want to go with a single four hundred instead of dual 250s so that you can supplement the mh with more fluorescent. 
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90 gal with 55 gal sump dual 250 double ended hqi 14k geisseman, 33 gal prop tank geisseman 150 hqi 14500k,two cpr refugiums,P.M. calcuim reactor,tunze wavebox.
12 gal nano
55 gal freshwater planted/jaguar tank with sump, pc lighting, co2 
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