Hi 420weedsham,
Since you havent had many replies, and no one has pointed you in the direction of any thread showing images of leaf deficiencies, (used to be a sticky for threads like that in the day) I am going to take a punt, and give my opinion and advice please take or leave from it what you will.
Looking atthe image the plant is in coco and a material type of bag ?
From that I gues over watering shouldn’t really be the issue. The plant looks recently stripped back for either trigerring or had cuttings taken or both.
You have probably fed the plant up to 1.4- 1.6 on EC to get it to that point, then stripped back.
When you do this you have to consider the plant material that has been removed was using food, water, and creating humidity as it breathed. Now thats been removed the plant is still in the same level of food ( too high now ) so needs to backed off a bit or a drink only (not flush but 0.4 ec for a while) help remove the higher food that the plant could use to photosynthesis with all those now removed leaves.
Because the humidity will have become lower the plant cannot handle the temp as high as it could with higher humdity, the leaves are not there to be able to process the food and water so you get tip burn (nute burn) the ands and edges of the leaf curl up due to the low humidity and go brown from the nutrient burn
As Stretch has said move the lamp higher, increase humidity and/or spray with nitrozyme or similar product seaweed based.
There does appear to be a deficiency in the green parts of the leaf, this could be from a multitude of things, such as lock out from over watering, possibly watering same as before stripping back, there is not the same leaf to breath and use the water. PH as stated by others and yourself that your pen was out of calibration. The petiol of the leaf stem looks dark but the vein of the leaf is still green, the new growth tips look ok too.
Lift the light, increase humdity, back off on the food a bit, spray with nitrozyme or similar. Should be good to go then.
Best of look keep us all updated.