[MaximDim]

I'm in the process of setting up my CO2 controller and trying to determine 'optimal' pH value for my aquarium. Now my water has pretty high kH (about 5 or 6 right from the tap), so looking at the chart (http://www.plantedtank.net/forums/attachments/water-parameters/812d1107560221-co2-chart-co2-chart.gif)
it seems that my pH should be in around 7 range. But than I should hardly need to add any CO2 to stay that way. Does it mean that my water is already saturated with CO2? Unlikely I think, so I guess I'm missing something fundamental in my understanding of how it works.
Would appreciate your thoughts.

 

[Rex Grigg]

If you are not injecting CO2 you don't have any. You need to test tap water pH after it has sat for at least 24 hours. A KH of 5 or 6 means you should have a pH around 7.6-7.8

 

[MaximDim]

Ok, so I let tap water to stay 24 hr and measured pH with Pinpoint monitor - it showed 7.5. Looking at the chart, I guess I'd have to inject CO2 to keep pH somewhere around 6.6-6.8 - does this sounds reasonable?

 

[Rex Grigg]

Yes. But I would go for more like 6.5 to get 30 ppm.