I've got 9 shrimp in my 29 gallon tank. I don't consider that they need more O2 than fish, what they do need is good water conditions.

I run my CO2 24/7. I allow the output from my small ecco filter and the small powerhead at the other side of the tank to ripple the surface. I like the current of water within the tank and consider this beneficial to all the flora and fauna within. I achieve an estimated 25 to 30 ppm of CO2 on one bubble per 1.5 seconds. I don't consider that I am losing a serious quantity of CO2.

I can't help you on the controller but if I was setting one up I would have it turn the CO2 off during the dark period rather than have it conrolled by the Ph.

Ian