Diagnosis of mistake and solution (I think overfeeding)

I will say ph is your problem give them superthrive and some cal mag

Your runoff ppm isn't very high and 5.7 is perfectly fine in veg for coco. You might wanna push it a little higher in flower. Is this just an issue on 1 leaf on 1 plant? If so don't stress it. Your diary Pic looks good.

This looks more like a PH issues on the leaves then an overfeeding issue. When I see PH drift in the substrate this is what I normally see on the leaves. I would bump that PH up to something aorund 6.0-6.2 I like it a bit higher aorund 6.2 as it gives room for the PH in the medium to fluctuate, Anything lower then 5.8 is entering PH lockout range and anything higher then PH 7.2 is also lockout. Some nutrients for the plant will not function well outside these ranges, it is also hard on the roots to have something that acidic. I also don't think a PPM of 335 is to high, if you're on a 500scale that is only 0.71EC 500 scales mean for every 500ppm=1EC, some TDS pens use a 500 or 620 or 700 PPM scales. most in western world use 500. its always best to ask the manufacture of your device to find out what one yours is using if you can't find it in the paper work it came with. Also best to use EC as 1EC=1EC across the board on all devices in the simplest terms. If anything your plants are likely a bit hungry as they looks a bit lime green to me, but photos can be misleading. In veg cannabis can take lower feed, in flower its going to want a bit more. For now keep up what your doing plants are looking descent. One other thing I would say to try and maybe lower the light a bit or increase its intensity as they look a bit stretched. I try not to feed antyhing over 1.2-1.4EC in flower and in veg max out aorund 0.8-1.0EC if the plants big. https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg here is a leaf chart if you noticing anything going off. Good Luck!

Why u think its overfed? You can check several website and they all go for way higher PPM. I use soil, no coco and my PPM i feed is 600 and runoff is like 800, since is use plain water every second time. But you need little bit higher ones, because soil gives like +100-300PPM with the included nutrients. I would go for 700PPM feeding in veg and up to 1100PPM in flower, runoff is always bit higher. You can check simple feeding shedules from nutrient-brands they give you an EC/PPM week per week. "Coco feeding shedule "your favorite nutrient brand""