Hi my plants are starting to yellow particularly at the bottom some leaves are dead

24/7 with FC 3000 is too much unless it is further than normal from canopy, which "12 inches" is not. I'd wager this is light related, if the info in diary is correct. That's a big boy/girl light. It provides a high PPFD at 18-20" from canopy and 18/6 light cycle... in fact, without co2, you may need to dial that to 66-70% on an 18/6 light cycle. If yo've never used a professional grade light, it is a whole different animal to thos midrange LED units out there... this light is half-step away from top-shelf. it's a really powerful light compared to most out there at same watts. 300 * 2.7 = 800+ umol/s. With ambient co2 you need maybe 70-75 per sq ft for 12/12 cycle and that's 11-12 sq ft of "max dli" coverage for 12/12 cycle and 33% sq foot coverage on an 18/6 cycle, which means you can use this light to vege plants in a 4x4 or autoflowers in a 4x4. run 1200-1300 ppm of co2 and control temp/rh and you can push 100+ umol/s per sq ft. Figure no more than 25w/sq ft with that light in vege... and then adjust from there. When/if you do a 12/12 cycle, that's when that light is great at 100% and 18-20" away... it'll provide nearly 40DLI eye-balling it/memory. (32-35w/sq ft on 12/12 schedule) (added co2 is 25-33% bump to these suggestions) all of that stuff is proportional. read up on DLI (daily light integral, umol/s, ppfd, ppe, ppf..) to better understand how we energize a plant with light.. it is ordinal.. it is measurable.. it is proportional to time. giving more is not alays better. Relative to environment, the plant can only accept X DLI per day. Around 40DLI is maximum for ambient CO2 and loosely controlled environment that avoids super cold or super hot etc but does not tightly control VPD completely. In fact, that suggesion is pruposely erring on high side, because we can always dial back a bit with height or dimmer but cannot manifest more radiated light out of thin air. See 2nd pic in question -- tacoing to reduce surface area and light damage that will only worsen if you don't adjust. The plant is probably super droopy for hours before lights off, i assume too? that will take care of the massive wilt going on all over the place.. not sure why leaves are dying at bottom.. get your light in order to better diagnose and not confuse symptoms. Leaves are shed naturally from time-to-time so if it is isolated, it is no problem.