Can you spot the difference?

Watch the video, can you spot the difference? One in the left video the sensor is working, in the right, it is not. Why?

What are we even looking at? Two side by side videos of the same sensor, a Deepsea Durafet, in a beaker of seawater. 
What is that? It is a sensor that allows us to measure the pH of seawater. See the square part with the screw in each corner... in the middle of that is a little hole, that hole has a microchip in it that is the part measuring pH. 
Why do we care about pH? It impacts lots of chemistry going on in the ocean. Such as clams or coral making hard parts like shells out of calcium carbonate. Humans are changing the pH by adding CO2 to the atmosphere making it harder to make these hard parts. Google "ocean acidification" if you want to learn more.
Back to the sensor video. Look closely at the little hole where the pH measurement happens. It is slightly shiny in the left video. That is a tiny bubble on the surface of the microchip. The bubble blocks it from the seawater and makes it stop working. (Good job if you could see that on your own!) 
Summary: Bubbles cause problems!
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