Leafs turning purple

It's looking like cannibalizing itself slowly. Needs feeding OR the PH of the media corrected. With 3-4 weeks left, I'd say you need to keep feeding it and perhaps a higher concentration. Lots to consider tho, like how much nutes. I look at ur journal. In week 5 of flower your buds should be bulking, and they do look fat. But this is pineapple express..its a hungry plant . Week 5 and 6 is when it should be fed the heaviest. Your looks like it's been flushed with strait ro water for 2 weeks and endured some really cold nights. My guess is they are trying to bulk up and canabalizing itself (yellow leaves) to make up the NPK deficiencies. Taking nutes from the fan leaves. Check the ph of your soil. If it's consuming itself, it behaves like nute lockout but in reality it is using up the nutes within the plant as ph off can lockout acess to the nutrients. Burnt tips on some fan the leaves suggest a slight high nute at some point but i think this is NOT todays issue. It's starving IMO. Need to find the cause. Ph or lack of feed. If you were alternating water feed schedule before, you could try a feed feed water cycle of the same solution if PH of media is good. In soil the nute companies schedule are per week. I'd take a week 5 schedule nutes chart, if was drying out and needs feeding 2x per week then I'd feed at 30-50% of that schedule, each feed at 1/2 the weeks requirments, depending on the size of the plant and how fast its growing. The whole plant yellow leaves suggest not enough N. The purple can be potassium deficiencies as well, especially if the purple is almost black. If you can verify the 20 deg nighttime temps aren't actually colder. Cold temperatures during lights out can turn a lot of strains purple (18-19)deg. Only takes a couple of nights to start that. If you find ur nights are colder than your meters' calibration point, then I wouldn't be concerned about purple at all. If the temps and PH are correct, then I think it needs an increase in balanced PHed feeding. With insufficient nutrients, PH off, or lockout, it causes an imbalance. You can have all the correct nutes, and if the ph is off, the plants' roots can't absorb. Then, the plant tries to get the imbalance from its leaves, causing yellowing as it take the nitrogen and maybe iron from them. Different nutes prefer different PH. But if you can get your media checked to be sure its 5.8 -6.5 then you know u just need to feed it more. If the PH is off then next watering flush with a 20% PH solution, balanced and then properly PHed full feed at the same event. Then feed with the recommended dose. If your PH is on point, then increase your feed by 10% but stay within the nute company schedule. It's too late to watch new growth for health but you should see some green return to your fan leaves. I used to see this when growing in fox farm soil, and near end of the grow everything was imbalanced as the soil was depleted of some of its nutes but EC was still very high. I learned when going from a charged soil to a feed schedule, flushing the media was required. Also, I doubt at 50%RH you have any mold concerns. This doesn't look like a root rot or root bound problem either.. Your leaves would be twisted molted yuk and buds wouldn't be so hardy looking. To sum it up You're in the home stretch with 4 weeks to go..hope my info can help you find root cause. At the end, reading back my answer, if temp and soil PH is correct, feed more or more often until ur pistils gradually turn brown. Then cut the nutes with a week to go. (Majority of trichomes are cloudy) Flushing is a controversial subject. Do it, or don't if you can keep your plant alive until harvest your buds will be awesome.