awesome!, the 2 stones is more than plenty, one would have been fine, but i imagine the roots are loving it. you should see an explosion of growth compared to other methods. i also use a bcuzz root stimulator/hormone in with solution it seems to help give the roots a boost and for me the difference was phenomenal.
A 2 gallon system should be fairly stable. youll have to compensate for a lot of evaporation though with those bubbles coming out the top, actually if you start seeing a problem with too much evaporation you might take one of the stones out and calm it down a little.you know what i mean? and as it evaporates the concentration of the solution with go up. i just use plain tap water as it evaporates. then after my solution has been thinned down a little, maybe after a week of adding water i change the solution and start all over again.
so in eccense, you start with high nutes in a fresh batch and gradually taper off througout every cycle that way it never gets burned. and i usually dont even adjust ph i just let it go. by the time the solution is thinned out its time to change anyway so that takes care of everything.