Ryan informed me at 20:48 UTC (13:48 PDT) that he was getting a PSL Chiller alarm, a likely indication that the level was low.  I had to watch the chiller for several minutes as the level slowly moved up and down with the regular flow of water in and out of the reservoir, but sure enough the water dipped just below the threshold and the chiller threw a Low Water Level alarm.  I added 150mL to get the reservoir to the Max line and the alarm went away.

We are averaging ~180mL of water added every 6 weeks, this has been fairly constant since late-April 2023.  I'll be in the enclosure tomorrow so will be able to do our customary leak check (a habit that's developed since we don't go into the enclosure unless necessary); I don't expect any leaks since the amount of water being added has not accelerated, but it's good practice to check while I'm in there.