That does not sound like a lot of CO2 then if it only goes up 0.25 during the 13hrs that the light is off. Especially since you have 3.8wpg on it for 11 hrs. Ohh, are you using T5 lighting?

My tank goes from about 6.8 to 6.3 daily. That's a 0.5 difference. Maybe it is because I have more surface agitation than you? Your tank does look pretty calm. How are you pumping the CO2 into the tank after it's been through the reactor?

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--->Pictures of my 75g Amazon tank<----