Yeah I meant PH! Yeah it lowers it pretty slowly. If you are using a DIY yeast setup it shouldn't matter, There is very little risk of overdose co2 using this kinda setup.You can overdose using pressurized co2. I've done it before and it's not good. I killed a very large colony of cherry shrimp and came close to killing the fish in that tank
. Though that was my fault, it should not of happened.
In regards to the PH thing, I wouldn't worry about it. My tap water is 7.6 and the tanks w/ co2 run at about 6.8. I still run pressurised co2 and it gets turned off at night, I don't know how much the PH "swings" at night. But cherry shrimp, rainbows, and gouramis have all been bred in that tank, so it doesn't seem to bother the fish. Keep in mind in the wild PH can fluctuate quite a bit
The only time you should worry about ph dropping is if your water has very low buffering levels. I'm talking about KH, low KH levels and your ph can fluctuate widely. High KH levels and your PH won't move if you hit it with a brick.