Have you considered all plants take in co2 and give off oxygen during daylight hours and take in oxygen and give off co2 during the night cycle. Since co2 is heavier than air the position of your sensor may be the problem if it's too low to the floor....just a thought.
Go with the Big picture rather than focusing on the little one which is a common mistake. Your plants look extremely happy, your stock, branches and leaf stems show No signs of stress, deficiencies etc.
As Bukvicak said "it looks like a jungle" (your canopy is Thick) and that gives insight to...
Start over or continue nursing these plants?
This advice is blunt and nothing like what's been given so far.
Your "oops" on your PH is your biggest issue and until you have that straightened out it won't matter what you do or throw at it (ppm really isn't relevant when growing in soil). Aside...
I use mostly soil but to me your right on about a PH issue. The fact you have the reds on both your stock and leaf stems including the veins of your leaves along with the necrosis usually indicates a phosphate issue. So either bad PH is blocking P absorption or your medium is lacking it. Since...
Rather than chemicals oils etc try this method I just finished posting on another journal. This is really effective if growing in soil, hydro setups I'm unsure if this can be done but may have some info that will help.
I have dealt with these pests a couple of times and refused to use chemicals...
I have dealt with these pests a couple of times and refused to use chemicals or neem etc. If your growing in soil this method is extremely effective as I've wiped them out both times. Since two of the thrips life stages are in the soil I reasoned at the time that interrupting or wiping out 1 or...
Yes all three will help, amount needed per gallon of water should be on the back of the bottle and use a PH up solution as nute's drag the PH way down
From the amount of red (anthocyanins) on the veins and leaf stems and yellowing on the lower leaves you may have a bit of a nute lockout. If your...
If your already 5 weeks in flowering you should be fine trying a little more P, your plants look healthy over all. Don't sweat those few rust spots at this point.