Hi There,
I have a 100 gal planted tank, and the Co2 is controlled by an aqua medic Ph controller is this the correct way of doing it ?. And what should the ph be set at ?.
Cheers
Pete

with a Milwaukee PH controller, i run mine at high 6.8 to low 6.9. i use a co2 ph chart to find out my co2 ppm. in my tank the KH is at 7 and with a at PH 6.8-6.9 my co2 is at 26.437ppm. (i got this info at http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm)
there is a lot of great info on these pages.

The PH controller is just one way to control the CO2. Even with the PH controller you need a needle valve to adjust the bubble rate - if it is too low, you will never reach the PH you select, and if it is too high the PH will overshoot by too much when the controller shuts the CO2 off. You still need to periodically measure the KH and make sure the PH you have selected gives you the ppm of CO2 you want. If the KH varies, the ppm of CO2 for a given PH will also vary. Personally, I prefer to do without the controller, and just manually set the bubble rate so it holds the tank at the ppm of CO2 I want, then use the solenoid to shut off the CO2 when the lights go off.

I hooked up a pressurized CO2 tank with Rex CO2 reactor I didn't know the concentration or how to go about it. Checked out D&E Aquatics's post above which led to Chuck's Planted Aquarium page which was a god send for me. After checking my Ph realized it had fell to 6.4 and my Kh is 2 or 35.8 ppm. My CO2 count following his chart is 24ppm which is in the green and good. I just hope my Aquarium Pharmaceutical test kits are accurate enough.

When KH is as low as 2 you can improve your accuracy a lot by using twice as much water as the test tube calls for - I just fill the tube twice and dump in it a small and thin wine glass. That way each drop equals 1/2 degree of hardness instead of one degree.