What to do? → BF Runtz Auto - Day 42 - RH70, 80F in BioBizz Light Soil

Hi 👋 I am guessing the same, salt buildup but perhaps a nutrients deficiency. When only older leaves seem to be effected, good stuff is being moved around to other parts of the plant in an attempt to keep healthy parts healthy and keep the sickness in the effected area. There seems to be red/purple stems on some of the fan leaves, indicating maybe a phosphorus or magnesium deficiency... Honestly, I wouldn't wait and I would flush right away, but I do admit that your plant looks to be in general good shape despite the effected areas. A few days ago I noticed a similar issue on my own plant and flushing was the immediate action to help the situation. I did it at night, close to the time when my lights turn off (cooler and less intense light = less stress on the plant) and left her alone until the next morning when the lights turned back on. Next morning I foliar fed at 25% strength to get nutrients directly into the plant tissue for a speedier more localized recovery. I wanted to feed her soon after flushing so she wouldn't be hungry on top of not feeling her best. She did very well and was thirsty in 36-48 hours afterwards, which I took to mean she was recuperating properly. I think flushing sooner rather than later would really help, followed by very gentle care and feeding for the next couple days. This part is key, being gentle for the following couple days to ease her on into recovery and recuperation. Such good luck to you and your plants 👋💚🙏