First try

If u want to just monitor not control I recommend CO2Meter RAD-0301 Mini CO2 Monitor. Amazon has it for 69 dollars. If u want to control I recommend Titan Controls Preset Carbon Dioxide (CO2) Monitor & Controller, 120V - Atlas 2 for 233 on Amazon

Hi @dillious_786! I guess it only affects the oldest leaves at the bottom? Purple stems, brown spots, coming from the bottom ==> this looks like a Phosphorous deficiency. This means either you didn't gave enough blooming nutes (Phosphorous) during the last weeks, or you might have a root pH issue. Growing soilless, you should stick into the 5.5~5.8 pH range, the pH of your last meal was probably not acidic enough for the rootmass to manage Phosphorous uptakes. Hope this will help, let us know how this goes, and happy growing! 👊

I'm sure your plants are down by now. The latest information I have seen on this topic is a departure from what I had accepted as fact. A "pro-organic" biologist, who was talking about organic growing methods, mentioned one reason organics really aren't better. He said people think that growing organically saves them "the flush". But he pointed out that plants cannot take in chemical salts -- only the ions of the individual elements. As a result he said flushing is never necessary or useful to remove salts. I know chlorophyll is good to reduce anyways. Flushing will do that. But chlorophyll can be broken down in the curing process as well - freeing your grow room up for the next crop. Aside from this one comment, the rest of the 90 mins was in organics: bacteria, fungi. nematodes and the like. Chemical salts can build up in soil and chemical ions in water making either toxic. I think this is because the plants has trouble competing for water with the salts/ions. They need to be flushed, diluted or changed so the system can be used again. The best method for determining when harvest is to use a jewelers loop or other magnifying system. Look at the droplets at the end of the trichomes. Each is first clear, then milky, and eventually amber. A common time to harvest is when there are an equal number of clear and amber trichomes heads. Harvesting when there are more clear trichomes than amber ones (early) will tend to produce a more uplifting high. Waiting for a predominance of amber trichomes (late) will lead to more couch lock. Adjust your harvesting criteria to suit your preferences. All your dry weight results are belong to us!