GiveMeABMW wrote in message
...
What kind adds the most oxygen... between bubble walls, air stones, discs,
etc.?

Also with the stones, is it safe to put them underneath the substrate?

And how many of whichever kind is best would I need for a 29 gallon tank
with 2
fish? Thanks!

For all intents and purposes, none of your options adds measurable oxygen to
the water. Their prime purpose is to circulate water so that carbon dioxide
can be exchanged at the moving surface for oxygen.
If your filtration is adequately sized and properly maintained, you may have
no real need for airstone type products other than perhaps decorative?? If
you do go with whichever (your choice), they can be buried just below the
substrate surface.

Jim