How long does a bubble bar airstone last in an aquarium?

A bubbler does virtually no good to your water. It's far better to attach the air pump to a filter and to get some real water improvement benefit from the airpump. I would not waste my time or money on an airstone unless I had a special reason for using one. You really must follow the basic rules of sucessfull fishkeeping if you want to keep fish succesfully. The basic rules are . :- 1 inch of fish must have at least 1 gallon of water. :- Every tank must have a permanently running 'cycled' filter. :- Every tank must have at least 50% of its water replaced every week.