I am using fox farms coco loco first time ever using it and I did not pre rinse it
Ok, I only say it because I've had the misfortune of dirty coir more than once.
I'm not going to suggest that it's dirty coco and to get right on to it. But if you keep getting inexplicable lockout, dry sandpapery leaves, or rust spots on the lowers I would consider it a possibility.
You say you're going light on the fertilizer and that's probably a good place to start to be honest. I can only really suggest how I'd go about it myself and that would be top dressing a small amount of dolomite lime on top to start. I would keep an eye on them for a few days and take things from there.
If there was no obvious improvement after a few days, measure the EC of your waste and see if there's much difference. If the coco is dirty and leaching salt, the waste EC will likely be a fair bit higher than your input.
If the EC was about the same or lower, i'd consider increasing fertilizer amount, or adjusting it's profile.
I'll be honest too, I found lime to be much better than just adding calmag to my nutrient. For the reason I didn't have to continuously feed them throughout the day. They would be fine for several weeks, but slowly deficiency would start showing up and i'd have to be feeding several times a day, just to keep them healthy looking. Limeing the coco after i'd rinsed it before potting up helped a hell of a lot. Watering several times a day became 1 or 2 at the most. Supplementing calmag went way down too.
That's my 2 cents and for what it's worth, it was large block form coco and from the local hardware. Though still majority of coco coir will all come from the same sources and depends on how well it's been washed and prepared for sale by your supplier.
As I say don't take this post as something to act on straight away, but if you keep having the same thing happening and feel like you can't figure out why, i'd question the coco.
Good luck and all the best.
