First off, if you're in coco, you need to feed your plant! Don't back off the nutrients. Those telling you this don't grow in coco or they wouldn't be giving you this advice. Your coco, on its own, imparts NOTHING to the plant.
Secondly, you should be feeding the plant every day...with feed, not plain water. This isn't a soil grow, so don't treat it as such. Up your ppm...my tap probably has a higher ppm than 150 all by itself...and your plants need more than this.
Thirdly, get your pH meter working, or get the drops or if nothing else, get some litmus strips...but you have to be checking your pH in this type of grow....5.8 is where you want to be with a slight swing up to @ 6.1 if it happens. (Using tap water vs RO will help in keeping your feed solution stable in terms of pH).
And if you can't pH your feed manually without causing a pH lockout...get a new feed. Not making light of your choices in feed, but if it sounds too good to be true, it most likely is.
I think if you'll adhere to these simple ideals you'll see your plants rebound. Good luck.