liv,
260 litres, that must be a massive tank. what are your measurements in cms.
i have a 140 litre tank an have a Sonic 9902 pump (cheap at $26.00) and run 2 air lines into my tank. i've placed regulators on the air lines as it was creating far to much aeration so i had to decrease the amount of air pumping into it (not to mention the noise of the bubbles rising to the surface).
also, you don't necessarily need the very big or long air stones as i have found the long ones (blue coloured stone) isn't all that great at producing very tiny bubbles. i personally think the grey air stones (which are less brittle) are very good for producing small bubbles.
peter.