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Dear Christof,
That movie looked like motion and it seemed oscillatory.  Is that a peristaltic pump with a stepper motor?  Other questions would be whether there is a temperature difference between the propionate solution and the other solutions;  size of tubing or differences in tubing adapters and couplers that may affect velocity or pressure, or differences in how the tubing is looped?  what is the shape of your chamber?  Diamond shaped chambers seem to have better mixing than round or square.  Improved mixing may allow a reduction in the flow rate.  Maybe test a reduced flow rate and see how that alters the shift, and compare to gravity flow.  
Glen MacDonald
	Core for Communication Research
Virginia Merrill Bloedel Hearing Research Center
	Cellular Morphology Core
Center on Human Development and Disability
Box 357923
University of Washington
Seattle, WA 98195-7923  USA
(206) 616-4156
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On Mar 20, 2013, at 4:17 AM, Christof Schwiening <[log in to unmask]> wrote:

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> 
> I really do doubt that it is real physical movement, but I will test it. If it is 
> movement then there are only two things that could be moving: the objective 
> or the glass slide. There is not much I can do about the objective but I can 
> take greater steps to make sure that the glass slide does not move. It is 
> already clamped into a standard microscope X-Y stage - but the glass slide 
> might flex or the whole stage might move. I will attempt to test this by 
> directly attaching the slide to the microscope. Although why this might only 
> happen when 20 mM propionate (or other organic) is washed into, or out of 
> the bath I have no idea. The movement is not coincident with the valves 
> switching solutions but occurs with the appropriate delay for the arrival of the 
> new solution from the manifold. There are no air bubbles and the movement 
> does not occur when I switch between solution lines containing the same 
> solution....