Buying an aquarium that is too small is a big mistake when keeping Oscars. Oscars grow quite large and need lots of room swim around. When I had a Tiger Oscar he lived in a 55 gallon aquarium and that was pushing it. My Tiger Oscar grew 11 inches long. The dimensions for a 55 gallon fish tank are: 48? x 13? x 21? – 48 1/4? x 12 3/4? x 21?, so we were cutting it very close. Also, Oscars can be roughens and can knock their aquatic environment apart if they are kept in close quarters. They really need space to move around to be comfortable in their surroundings.
These Albino Tiger Oscars will soon outgrow their present tank and need to be moved to a much larger environment. Finally, Oscars are a big fish and will add significantly to the bio-load of the tank. This means that you will need a lot of water volume to maintain a healthy environment and 30 gallons of water are not quite enough. If you start out with too little water, you will develop water quality issues very early on and it will be a big challenge to keep your tank suitable and stable.