Think what you mean is the difference in bubbles they make. Some are made of more dense material (sand grains) = smaller bubbles. Than there of course is a size difference. Nothing wrong with those ones but if you like to make a kind of bubblewall you'll need bigger ones.dyunoy said:I have a tetra wisper 40 air pump and I was looking at airstones to use with it but I've never used them to understand which airstone is the best to use. I was looking at a few things on Amazon can someone please explain to me how it works and recommend a good airstone(s)?