An airstone is only going to make a tiny bit of difference, but if your CO2 is at 0, would be of a theoretical benefit. Kind of like how plants will pearl after a water change from being exposed to air -there is CO2 in atmospheric air, just not a lot of it. A weaker air pump or a gang valve to bleed excess pressure off would slow the flow rate if you needed. But again, this isn't likely to make a noticeable difference.
Yeah, often happens that when you eradicate one algae, another comes along. If nutrients are there nature will find a way.
Nothing good happens fast in an ecosystem.