Just what constitutes a big tank?  Obviously, if you've been used to keeping an 18"x12"x12" aquarium (not recommended for marines by the way) then obviously a three foot tank is going to seem relatively big.  However, I would say that the realm of the truly big tank begins in the region 5'x18"x18".  This represents 70 gallons gross gallonage of water and holds all the advantages, and the disadvantages, of a larger aquarium.

An article discussing the proper stocking of a four foot, fish-only, marine aquarium.

There is no doubt that marine fishkeeping can be great fun, even when there appears to be nothing to do but wait. Let me explain. Imagine you have purchased your first marine aquarium, it is set up and running and the maturation fluid has been duly added. Now you imagine there's 3-4 weeks of utter frustration because you're completely idle until those ammonia and nitrite test readings drop to zero and you get the green light to go out and purchase your first fish. Wrong! It may just be some of the most enjoyable and educational days you spend. For in those four short weeks you may choose as many fish as you like without getting out of your armchair, spend money like water without reaching for your cheque book and make mistakes galore without the need to pay for them. I am, of course, referring to that period of time when you actually plan the living contents of that all too empty aquarium!

World Conservation Monitoring Centre provides objective, scientifically rigorous and focused information on global biodiversity and the sustainable use of the world's living resources.

Since 1993, UNEP-WCMC has been developing the most detailed global map of coral reefs. This information represents a critical part of the increasing information base now available describing coral reefs world-wide.

Cyanide Fishing Destroys Coral Reefs

Cyanide, one of the most toxic poisons known, is being used to catch live fish in the South Pacific and Southeast Asia. Fishermen stun fish by squirting cyanide into the reef areas where these fish seek refuge. They then rip apart the reefs with crowbars to capture disoriented fish in the coral where they hide. In addition, cyanide kills coral polyps and the symbiotic algae and other small organisms necessary for healthy reefs.