it could definately be a problem. i dont know how heavlily your tank is planted but if you have co2 and a good amount of light it wouldnt take long at all before your tank uses up all the nutrients. you bottom out and you'll have an algae problem for sure.
if you do do a blackout without your turning off the co2, here is whats going to happen. your plants wont use the co2 that you are putting in there so your water will build up more co2(unless you are using a ph controller) and the ph will drop lower than what you have it set at now. on top of that your plants let out co2 at night. so unless you have a controller, your ph will change anyway. on top of that i'm not sure that the ph, when altered by co2, is effective at changing the ph in a proper way. what they are more sensitive to is tds (which has a direct effect on ph). if you have water with tds that cause your water to be at the ph of 8 and you lower the ph with co2, you arent changing the tds at all.
i'm no shrimp pro though so check over at the invert section. msnikkistar or mordalphus should be able to help you on that