I've used warehouse/manufacturing MH's over tanks in the past.  There are some issues to be mindful of:  The ballast will be magnetic, which means it will humm.  It will not be enclosed (I doubt you want to use the entire enclosure) so you'll have to figure out a way to enclose it.  Depending on age and type, it may be a set transformer meaning it can only handle a certain incoming voltage...normally 220 but could be as high as 480.  These can't be modified.  If it has a "multi-tap" ballast then yes, you can wire it for 110 applications.  The next thing is it will be HOT!  You'll need to figure out a fan or it will overheat and shut down.  Finally...you'll not use the original reflector but at least want a cheap spider reflector.  That's what I ran mine with until I upgraded.  I'm not saying it can't be done but unless you know what you're dealing with, it may not be worth the money or hassle.