# does co2 lower or raise ph



## obet_07304 (Jul 23, 2006)

CO2 normally lowers PH.


----------



## dannyboy (Jul 20, 2007)

thanks im just trying to under stand how the ph controller works i just got the sms122 ph controller and dont under stand how it controlls the co2


----------



## evercl92 (Aug 15, 2006)

CO2 is technically an acid. The amount of pH drop is dependent on your water's hardness, and which elements make up that hardness. This is why GH and KH are important. 

My understanding of the pH controller unit:

You set it to a certain pH - determined by what CO2 concentration you want, and your actual KH value. This can be determined by the chart found on the calculator found here.

The controller will continue to leave the solenoid open, allowing CO2 into your tank, until the desired pH is achieved. Then it shuts off. When the pH value increases, the solenoid will open - long enough to drop the pH back down to where you have it set.


----------



## sandiegoryu (Feb 15, 2006)

Actually, CO2 is a base, H2CO3 is the acid . CO2 dissolved into water turns into H2CO3. CO2 is the conjugate base. :-D.

And I thought it was only KH that mattered with how much PH moves. GH isn't supposed to matter, but IME, high GH usually follows with high KH and low GH follows with low KH unless something artificial is added to increase either thing.

And you use that chart, and with your KH value, which you need to test with a test kit, you find the ph that has the CO2 ppm that you desire, and set it there.


----------



## cody6766 (Mar 15, 2007)

> Actually, CO2 is a base, H2CO3 is the acid . CO2 dissolved into water turns into H2CO3. CO2 is the conjugate base. :-D.


yup, in layman's terms:
carbon dioxide + water = carbonic acid => lower pH


----------

