[Darkblade48]

Originally Posted by blackandyellow

My tank currently has a PH of 6.5, a KH of 1 and a GH of 2, this is without any Co2, Ph is low because of the large piece of driftwood and KH is low because the tank was filled with bottled water.

Originally Posted by blackandyellow

My question is, since the tank already has a low ph and KH does this mean it has a good amount of Co2? How could this be possible if I still haven´t injected any co2 yet?

You essentially answered your own question. The tank does not have a good level of CO2 yet, because you haven't injected any CO2 yet. The pH and kH relationship works, provided there are no outside influences. However, in the aquarium, things such as DOCs and other chemicals will affect the kH/pH relationship, thereby skewing the estimate of how much CO2 is in your tank.

Originally Posted by blackandyellow

What would happen once I start the Co2 system? since it would be controlled via a ph controller would it be off all the time?

Essentially, the pH controller would read the pH as 6.5, and then turn off once it reached its set point. In most cases, the general thing to do is to measure the pH, and then set the pH controller to 1.0 lower than the measured value (in your case, 5.5) to get a good level of CO2. Since this is quite low, I'd perhaps adjust your pH controller to 6.0 first, and then go from there (i.e. adjust as required by watching your drop checker).

Originally Posted by dizguy

I'm just going to throw this out there and I don't know if it has been tried. I have read that fluctuations in Kh affect the CO2 / Ph formula. Why not isolate a solution of known Kh value like in a drop checker to use with a probe?

I suppose this would work, but I think it is overly complicating things. As mentioned, most people just set the pH controller shut off to a pH value 1.0 lower than the current pH and then go from there in adjusting theri CO2 (by observing the drop checker).