Testing out coco probably wasnt the best idea for my first attempt in a cup. Hopefully they shake off my murder attempt
Have you checked the run off, brother? With pure coco you want the PH around 6 and nutrients with every watering. 600ppm for the current stage would be enough. You have for sure a too high PH and a high PH is a sign for salt built up and therefor you have almost no cation exchange.
Flush them with ~500ml nutrient solution untill the run off has almost the same PH and ppm values like what goes in.
Flush her at least once in a week to remove salt built up. I do it right before the light goes off and in the morning they get 700ppm/PH 5,6-6,2 again.
Believe it or not but it's also my 1st coco adventure and I feed her 3x the day now but each time enough to cause as little run off. Its called coco drain to waste and when you feed 3-5x the day there is no reason to go higher like 700ppm.
So first thing to do is flush her and make sure the PH is around 6.
Do not feed her until the cups are almost dry.
Start feeding every day untill you have lets say 50ml run off. Remove the run off but check PH and TDS evry now and than and when the ppm starts to get higher its time for another flush. You can also try a feed, feed, water, feed, feed, water regime to avoid salt built up.