Im not using “stones” at all in my hydro system. Stones also tend to plug up over time, and they are a pain to clean, plus they are $.
Most importantly, you really dont need those tiny little bubbles. They dont add any more O2 to the water than a simple fluming setup. Just having a stream of bubbles lifting water from the bottom of the rez and “fluming” or roiling the surface works just as well or maybe even better as far as adding O2 to the water. Water falls also work well.
I made some “air non-stones” for my rez by just taking some small plastic tubing that fit my air lines, and crimping the end down until there was just a very small hole. Like the size of a large sewing needle hole. Maybe 1/2mm or so. You could also just fold over the end of the airline and then punch a small hole in the tubing.
I zip tied a piece of lava rock to the end of the airline to keep it on the bottom and thats it. I have 4 of them running in my rez.
Actually, since I have a piece of lava rock on the end I guess it is an air stone after all 