Recommended airstone for bubble scrubbing are wooden ones since they produce very fine microbubbles. For air pump I use a Hygger air pump for my phytoplankton grow out. It is more expensive than the super cheap Chinese ones on Amazon but runs noticeably quieter.
One thing I don't like about bubble scrubbing is the microbubbles result in more salt creep everywhere. Instead I use DIY coral snow once a week.