No water was added to the chillers. The values I saw on gauge actually read higher than what was reported on the 25th of June by about ~0.5cm. This was enough for me to look at the filter socks and double check how they were seated. Moving the filters into different positions did change the water level, but nothing outside 0.75cm. I decided not to worry about it too much and double check on them later.
I was curious if the rise in level could be from thermal expansion, doubtful but a good practice regardless. As the chillers find new lock points they will change the water temp by 0.1C steps at a time, and the largest difference I could find trending was ~1.0C. A quick back of the envolope calculation, assuming only absolute expansion :
dV = V0αV(T1-T0)
V0 = [36L] inital volume (alog30638)
αV = [0.00210 oC-1] coefficient of volumetric expansion of water at 20.0oC
T1-T0 = [21.oC-20.0oC] Change in temperature
We get a dV = 0.0075L. Not nearly enough to see in our 7L resevoir. This is with me assuming absolute expansion, not accounting for the change in the piping.