percula rapid gilling, fading color

[Mavrk]

I put a true percula into my tank as my first fish on Tuesday night. It has been doing fine until this morning. Now it is sitting on the bottom having difficulty swimming higher. It is breathing fast. And the color is slightly faded.

Parameters:

Ammonia 0
Nitrite 0
pH 8.3
Nitrate 20
Temp 80
Salinity 1.024 SG (this is a little low at 32-33 PPT)

There are diatoms in the water producing oxygen bubbles, but other than that, nothing has changed.