"Do It Yourself."  A great way to save a few bucks and expand your knowledge of design and construction.  Or the #1 cause of migraines.  Take your pick!  Personally, I like to experiment, design and build things.  I have access to most of the materials and equipment I need, so why not?

A saltwater tank requires heavy duty filtration.  Water quality is critical!   Unlike a freshwater tank, where the fish you buy are captive bred and used to captivity and mediocre water conditions, saltwater fish, for the most part, are caught in the wild.  This explains the higher price, as well as why some fish simply don't make it.  A saltwater fish goes through a lot of stress - getting caught in a net, stuck in a little bucket, then a holding tank, a bag, then another bag, shipment to a warehouse, etc...  By the time you get the fish, he's been through hell!