Which pH indicator will give a dramatic color change with small changes in the amount of carbon dioxide dissolved in water? I want to do a demonstration for students where they take a capped syringe and change the volume above a solution of seltzer water.  The amount of carbon dioxide dissolved will vary, hopefully changing pH enough to cause an indicator to change color, the more dramatic the color change, the better.

I have tried universal, bromcresol green, and methyl red with little success.  I can add substances to the seltzer water or change the temperature of the water.  I'd like a SAFE system I can create that will change color upon moving the plunger.
Try neutral red. It's transition region is from 6.8 to 8.0 > red to yellow

Also check this wikipage for other options.