The air bubbles is an indication of Cyanobacteria. This is feeding off excess nutrients in your system. You can get false readings when you test your water because the cyano
is eating up the nitrates really fast and they don't show up on a test.
The best solution is to siphon out as much as you can while you do a PWC
. Frequent PWCs is the best course of action against cyano
and other forms of algaes. Don't fret it happens to all of us. After my upgrade and tank disaster I'm just now starting to get mine under control.