2 Red Poison - Nutrients burn? Needs P / K ? - 3 and half Weeks and starts to flowering:

Start a diary - reconstruct as much of the grow as you can ... the burnt tips are from nute burn and even if you've corrected that issue, those leaves are not going to get better - they'll always look like that... Good luck.

Hmm.. i'd guess a K-deficiency, if you haven't fed often in coco. Really depends on what you have fed before this point and with soilless it sticks out like a sore thumb what is off. More importantly: if coco, it is completely devoide ot nutrients. in a soilless grow you want to provide fertilizer every single irrigation and have minimum 10% runoff waste water. put it down drain or outside is useful too, but not for potted plants. so, you'll want a well-balanced 1.3-1.5 EC feed... it can handle full strength when 'full' is this mild fairly early. I wouldn't go below a 1EC for seedlings / immature plants. 120+ N 40+ O 180+ K These are attempts to list minimal values. The 3 below will be impacted by whatever ca/mg comes in your water. Think tap can even have a bit of S in it? Ca 100+ Mg 80+ S 100+ *I know without adding it up this is a very low total... your tap water, environment, and genetics will tell you what more it needs, and it won't be anything requiring panic or a knee-jerk reaction. it'll be nice and slow. You can be certain, adjust, and observe high probability of fixing the issue. I have hard water, so my needs are different. You may need 130ppm of Ca to prevent any deficiencies, for example. Mg and S are easy to add with epsom salt (magnesium sulfate). any chep foodgrade version works. Use an online nutrient ppm calculator. simply type in % values off your labels and it'll spit out values. You don't have to do this every single time or even often. Knowing the ballpark you are in to start makes adjusting more easy though... Adjust proportions to react a 1.3-1.5EC mix... If you have a gist of this, any problems stick out easily. This is where a multip part mix helps.. adjust proportions of the part that most impacts what symptom is showing and reduces impact total balance of other nutrients as well. 2-3 part nute system is plenty. can always supplement as needed, but a good setup won't need it. If you need a bunch of supplements to keep a plant happy, that is a business ploy and nothing else to extract greater profits from mundane/ubiquitous things. That's a greedy AF brand is what that is.

Diary would be great but as the plant is very wee. It wouldn't need much in the way of nutrients so my guess, as that's all it is with no more data, is you are locked out So, as its coco. Flush it hard. Until you get back down to tap ppm.. then apply a light feed a few hrs later. 1-5-3 will do for flowering. Those types of ratios i mean. Flush and restart. Less of the Synthetic nutrients. Until you get it out of lock. Use few nutrients to get it eating again. Good luck

Elle a fleurie ta plante. Si je vois bien...