If you got a co2 bubble in your drop checker then you're not getting the right reading . For me, the drop checker is another thing to dink around with and has not *really* helped me determine how much CO2 I have in my tank. Plus my DC gets wonky readings cause I think my Gouramis are breathing the bubble out of it..
Have you determined your PH drop from lights off to mid-photoperiod?
I get at least 1 point drop (from 7.6 to 6.6) by mid-day.
If your fish are acting fine, then you need to bump up the CO2 or decrease surface agitation. My opinion.
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