Try keep your PH solid. Water and fert feeds.
You generally need to feed coco everyday. So don't start of too strong 3-400ppm will get you into a few wks of veg. Then up it as you need. You can follow up with a water feed if you don't get much run off as their might be leftover residue your plant can eat.
I'd suggest you do some 101 on coco growing as there really is a lot to it. And you'll be able to match things you read with the likes of your environment.
Is your water hard r soft....as this will be an issue (calmag) might be needed even before pre flower, all depends. Coco finds it much harder to store these things. Hence why they say feed everyday. I use 70% coco 30% light mix and every 3 days or so I only have to feed. I tried every 2 days with some and got burnt tips. So just a bit of light mix that's gen consists of mainly coco.
Good luck pal. Feel free to DM me r anyone who answers here will be more than happy to help you.
Good growing.