It depends on what your trying to accomplish, what your going to be keeping in it, as well as the material of the tank itself. Glass or Acrylic. You can have a Fish Only system, FOWLER system, or a REEF system.
Reefs are the most expensive and will run around $3,000 for a 55 Gallon set up Makesure you focus mainly on 5 things in a reef Aquarium and they are...
Water Flow
Lighting
Protein Skimmer
Berlin Style Open Sump
Large amounts of live rock (1 - 5 pound/ Gallon)
FOWLER (Fish Only With Live Rock) Is cheaper and will run about $1,500 for a 55 gallon Set up. Use ½ - 1½ pound live rock/ gallon
Fish Only, can go many ways, you can have a cheap hang on back filter or canister filter (Not recommended) or a below the aquarium Wet/Dry filter (Best Option). For a 55 Gallon set up maybe around $600 -$800 without a protein skimmer, though it is BEST if you do get one.
Saltwater weighs about 8.6 pounds per gallon, so 25 gallons of saltwater would weigh about 215 pounds in total.
1 gallon of water = 10 pounds so the water in the tank is 3000 pounds but all the rocks and decor take up space so there is less then 300 gallons of water but the decor and stuff weighs more then water
Roughly 8.5 lbs per gallon. You do the Math.
It cost $1.34 per gallon.
it will cost about 100 pounds
the weight of the tank will be about 100 pounds
At $3.00/gallon, it will cost $72.
$5,500 to $6,500
$1.16
Air bubbles will do nothing. What is needed is a filter.
I would think at least a 60 gallon aquarium
A gallon of milk cost $1.01 in 1958