I would disagree that you cannot over water coco. Daily watering of coco with waterlogged roots has not worked out well in our grow with results looking fairly similar to here. If cold temps and climate has been addressed and the plant still wont drink properly; evidenced by completely hanging leaves, OP should try to figure out why the roots wont draw water/feed when all other factors are inline.
If you have massive roots you can water your coco daily or even multiple times a day with very good results; flooding the pot means that when the water runs off air will be drawn into the media which is really good. But if there is a too much water in your pot when you water your roots zone can get into an anaerobic state and start rotting or just not working well.
Though i agree that one shouldnt let coco dry out completely, the last bit of water tends to concentrate nutes and burn leaf tips, i dont think that hydrophobic coco is such a big thing to fear if youre hand watering: just start your watering by wetting the top with an amount which wont give you any runoff. Leave it for a little while and then water again slowly until run off and your coco is not hydro phobic anymore. If you wanna make sure you can even take another break before you do the final until runoff watering. This would be a very manageable problem in comparison to anaerobic root problems.
The rules of coco posted above are not wrong, just seem to be tailored for a specific subset of coco grows:
When you have a pot full of roots and doing automatic watering. The rules would work fantastically if your plant was able to handle the waterings but in this case i think OP is likely drowning the plants.
Id add one point to it; make sure to water with extra heavy feed to buffer at transplant since coco tend to attract nutes leave little for the plant. Second watering go back to normal. Also since led plants tend to drink less than HID plants you can usually go up a bit nute strength compared to hid grown coco. If the plant drinks less juice the juice have to be stronger to get the same amount of nutes.
This means you really have to control runoff, primarily for EC is vital; how else are you going to know whats the actual EC of the root zone? If youve been overwatering with little transpiration and growth the coco is likely to drift towards getting hot with nutes.
It doesnt help that led lights and coco can be a little extra hard to get the hang off but really easy once you get the hang off it.
I dont really care to argue with anyone who has a different point of view here, just to provide a another perspective. Anyone who has a working system should continue doing things the way theyre doing it. But OPs coco grow is not working out, even though hes corrected environment and followed advice. Logic states that if the advice didnt work you need to try something different or revise thinking.
Ill trust my plants more than the guys on the internet. Which i guess is somewhat ironic cause i would just be another guy on the internet to the rest of you guys, lol.
Hope OP can sort this out. Anyone who feels offended by me being a bit contrarian to your advice; consider me saying youre partially right rather than completely wrong, im not here to start any flame war over small stuff, only to give another perspective