Last time I was on shift, we were filling the TCSy Chiller fairly frequently.  Went out to chec on both chillers.  

• X was fine.
• Y was a little low ("6.5 level").  So I took it up to "8.7" by adding 225mL.  Before topping off I could see an "air bubble" which popped.  At any rate--perhaps I could have added more water due to bubble effect, but opted to leave it as is.