Yeast will usually cloud the tank, additionally yeast seldom causes problem aside from the slime it leaves on everything. 30-38 ppm is higher than some folks reccomend but certainly not enough to cause trouble with the Kh level you have. Since you are using DIY CO2 the only good way to lower it is to increase agitation. water changes will only help temporarily, and the same situation will return in a couple of hours. I would look for something else amiss with the shrimp. My personal opinion after reading all of your info is that the CO2 is not the issue. This is solely based on my experiences, so I'll just say take it as opinion and nothing more.
Dave