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I must say that I continue to have problems with the Solent system.  I 
cannot get it to maintain the pH of standard unbuffered cell culture media 
overnight.  In this system, the 5% CO2 enters a humidification unit 
(within the outer 37 degree chamber) and then is delivered to the working 
head (the smaller sub-chamber that sits on the stage).  It's possible that 
the CO2 is leaking out from under the working head or through the bottom 
of the stage.  Currently, I am considering extreme measures to close the 
system from below.  
Evaporation can also be a problem with this system, especially during the 
dry winter months.