I have several plants that are about 4 weeks into flowering. The are losing all their green color and turning pale green and moving onto yellow. I grow 2 plants to a 15 gallon tupperware container with lava rock and a septic leach pipe on the bottom to aerate the soil. One plant may be losing its color while the other is great. There is very little leaf curl, In fact aside from the loss of color they look good. Some leaves are turning brown on the fringes while another plants leaves are getting small red and brown spots. I water with Bio canna so I know that pretty much all of my nutes are there. I grow under 600w hps. I am really confused at this point. I flushed several bins just to see if perhaps there has been a build up of salts or maybe potassium. I think if Potassium levels are too high that they may lock out other nutes. One more thing I just added C02 to my room, I run it at 1200 ppm 80 degrees and 55% humidity. Anyone have any ideas? I'm really bumming they were looking so beautiful.