# knowing the correct CO2 level



## searley (Jun 19, 2006)

i have a 40G tank, which i am putting CO2 in via fire extinguishers fitted with a regulator and diffusing via a ladder style diffuser, which is working very well, and i can put in as much or as little CO2 as i like

i am using a PH controller with solenoid to switch the CO2 supply on and off, im just not totally sure on the PH level to choose to get 30ppm

i have kust had an outbreak of Blue Green Algae, BGA, so turned off the CO2 and lighting, and covered the tank, its been covered for 3 days, and i intend to un cover it tomorrow

with the CO2 turned off the PH monitor is showing a ph of 8.09 so should i be aiming for a ph of about 7 when the CO2 is on??

until now i have had it set at 6.6


other details about the tank please comment if im missing something:

my lighting is High output T5's at 3.9wpg

i am dosing:

1/2 tsp KNO3
1/8 tsp KH2PO4
1/8 tsp traces

at water change i am also adding 1/4 tsp of a calcium magnesium mix at a 4 to 1 ratio

GH is about 160 KH is about 180
Nitrite and ammonia is 0
Nitrate is about 40ppm


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## darkoon (Jun 7, 2010)

did you calibrate your PH controller properly? did you add any baking soda to your water? 8.09 PH is pretty high. Run a PH test on your tap water first. 
assuming your GH and KH readings are in ppm, that translates to ~10dKH. and assuming your tap water PH is 8, your correct setting for PH controller should be 7. 
refer to this table for correct PH setting for your PH controller http://aquarticles.com/articles/plants/Podio_CO2_KH_PH_Chart.html


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## searley (Jun 19, 2006)

darkoon said:


> did you calibrate your PH controller properly? did you add any baking soda to your water? 8.09 PH is pretty high. Run a PH test on your tap water first.
> assuming your GH and KH readings are in ppm, that translates to ~10dKH. and assuming your tap water PH is 8, your correct setting for PH controller should be 7.
> refer to this table for correct PH setting for your PH controller http://aquarticles.com/articles/plants/Podio_CO2_KH_PH_Chart.html


Hi

Yes my PH controller is calibrated..

it has 2 probes, and 2 read outs and i calibrate one 1 probe one week and the other the next..

my tap water seems to read slightly lower at about 7.5
KH is also slightly lower in the tap water at about 80ppm

no i do not add baking soda

but from what you say it does appear that yes a PH drop of about 1 is as good as 30ppm, so i will set at 7 and see what happens

thank you for your response


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