Sick Flame Angel

[walts7598]

1 week ago, I picked up a Flame Angelfish to join my two clowns and yellow tang. He seemed to be acclimating well until yesterday when I did a 30G water change and vacuumed my gravel (which I do every two weeks). Now he is swimming on his side a lot. Can anyone give me advice on what I should do? Thanks!

Current water conditions:
Spec Grav: 35
Nitrate: 20PPM
Nitrite: 0PPM
Total Alkalinity: 120
pH: 7.8

Tank specs:
90 gallons
sump system
5MDQ pump

 

[melosu58]

A very important reading needs to be done. Ammonia?

 

[walts7598]

Picked up a kit, it reads somewhere between 0 and 0.25PPM. I know it's supposed to be 0, but is this high enough to cause problems? Is it possible I disrupted too much junk under the gravel (I don't usually vacuum the gravel as aggressively as I did yesterday). If this is a problem, what would you recommend I do?

A very important reading needs to be done. Ammonia?