I have been waiting to put a co2 system into my OEBT tank as it lowers pH and my pH has been consitently creeping lower. While not uncommon in a tank of RO water with Indian Almond Leaf and Driftwood I did not want to take any risks so when I added the CO2 system I set it to very low and added just a little Sodium Bicarbonate to the filter. I plan to pay close attention to the pH over the next week to play it safe.
Jason Wechsler
Orange Eyed Blue Tiger Shrimp Blog (OEBT) 
What substrate system are you utilizing? Most of my successful soft water shrimp were bred with Amazonia or Stratum as both lower your Ph. I use distilled water 85% and tap 15% mixture so give them some mineral content, but not spike the Ph to our tap of around 8. I have always been wary of CO2 without a monitor and solenoid to snap it off in case of the water shifting. Too many stories of battery acid in the tank I suppose, lol.
I am only using pH Neutral gravel and sand(about 60/40) pre fertilized with shrimp safe ferts. It turns out this is not really and issue because of the way this particular CO2 system was built. PH crashes from CO2 generally only happen at night when the CO2 runs but the plants can not utilize it because of a lack of light. (at least that is my understanding)
This particular system (http://www.amazon.com/Fluval-Mini-Pressurized-20g-CO2-Kit/dp/B0049RL3H4) is small and you can control an 4-8 hours supply easily the way the to air storage things work. It is fairly safe and easier to manage than a diy or canned yeast based system.
How much it helps my plants is yet to be seen.