Originally Posted by VaughnH

That is backwards: yellow means low pH or too much CO2 in the water, and blue means high pH or too little CO2 in the water. So, if the drop checker fluid is blue, add more CO2 by adjusting the needle valve. If it is yellow, reduce the CO2 by adjusting the needle valve. A bubble counter is very good when doing this, because you can see how much effect adjusting the needle valve is having.