To the dude with loads of microbubbles in his tank, just a quick pointer for you (never usually get involved in these thread "conversations" but wanted to let you know) these microbubbles are highy likely to cause embolisms in your fish ! a good flow with ripples on the surface or ideally a trickle filter is all you need for any size tank, unless its "surface area" is tiny ie deep but thin tank, blowing bubbles through your tank will cause you loads of probs and is a ineffective way of ensuring oxygen levels in the tank, 5-7mg of oxygen per litre is perfect anything over 9 is dangerous. Surface exchange is what its all about dude