[jedimaster]

Interesting post but the one calculation you forgot to mention was a tangs natural environment.
approx
2,000,000,000 gallons of water per inch of fish.

Now you mean to tell me that 5 gallons per inch of fish or 30 or 40 or 100 or 1000 is enough?
Obviously none are adequate. The whole point is that most people would like to give as much room as possible for any living creature. And for most people the largest practical size tank is 100 gallons, many people however choose to go larger, even better.
The fact remains a 27 gallon fish tank is too tiny, as is a 150 gallon tank. But if YOU were locked up in a cage for the rest of your life would you want it to be 27 square feet or 100 square feet.

JMHO