What coral species do you plan to keep? If your 10 gallon nano is going to be stocked with mostly SPS corals then it would not be too much. The more important concern is maintaining water quality and specific gravity. A 175 MH over a 10 gal would produce a lot of evaporation. It would only take a small amount of evaporation to create a large swing in specific gravity in a 10 gal.
well i decided to go a different route since that would be around 17 watts a gal. would a 250w 20k mh be okay for my 29 gal? or would that still be too much?