Adding ferts (Flourish) and iron (becareful with iron, Fe is toxic in high levels to fish) should help the plants; some plants use root tabs so that might be needed.

Good doing the large water change and vacuuming up the BGA is the best method.

So far, all is well - the car now works fine, the CO is zero, and I am catching back up with the tank. The commute will get far better when I move in the next ten months ... .