I see all sort of conflicting answers and answer with no supporting evidence.
I'm wondering how often you are watering, and what sort of runoff you are getting? I'm also growing (first time) in coco coir, and my plants have grown at an amazing rate.
I can't say what is causing your issues as I just don't have enough experience. I can contrast with my grow, which you can see in the post 'Explosive Growth in Coco Coir' to see how it compares to you.
Here are some things I think are fine in your case as they mostly match my experience.
1. RH and temps: My RH was high in the veg state (around 60%, higher at night when fan was off). Temps at 79-84F. Those seemed to be ideal veg state conditions, and my plants exploded in growth.
2. pH - based on advice from a number of sources I have set my pH at 6.0. I use a Bluelab controller to keep it at 6.0 in the reservoir. I use Silica Blast as the first ingredient in my fertigation mix, and it notes that pH should be set to 6.0 for that product. 6.0 seems acceptable across both veg and flower, and .... it's working for me.
3. Lighting - without an actual meter reading, we - and you - have no real ID what you're putting on the plants. Curling edges might be a symptom of too much light, but overall your plants didn't look scorched to me. Give us some sort of actual measurement please, lumens, LUX or PAR.
4. Coco coir type - what's in the pots? Homemade? buffered?
5. Cal/mag - exactly what have you been doing here?
6. Nutes - a bit more detail please. I started mixing nutes in RO water, with starting EC of 60 (my scale is micro siemens, so 1000x yours). First I put in 2/5ml/gal of Silica Blast, and then I wait an hour. Next is Cal/mag. I started out at 2.5ml/gallon Calimagic, but have dropped to 1.9 in flower, going my GH chart. This brings my EC up to around 350. Next I add the GH nute trio, which gets EC up around 1200. I then add a couple of supplements, Floralicious and Koolbloom, which gets me to around 1350EC. A bit of humic acid (DIamond Nectar), some Yucca powder as a wetting agents, and finally 2.5ml/gal of 33% h2o2 to keep the tank clean of algae. I mix up 10-11 gallons, and the pH comes out to about 6.1. I then put a bit of pH Down in it and dump it in my 14 gallon reservoir. I then usually top up the tank to 14 gallons with plain RO water to drop the EC a bit. I still have a bit of tip burn on the leaves, so it may still be a bit high.
7. Watering cycle - in veg, I started with 3x daily feedings, with 10-20% runoff. As the plants grew, the runoff quit, and I needed to go to 4x daily. When the runoff quit again, soon before flowering, I increased to 5x/day. In flower, recently, my runoff EC started going up and up and up - to as much as 800 points higher than input. So I went from 30 second feedings to 35 second feedings to increase the runoff. In 4 days the runoff EC has dropped until it is now about the same as the input.
My initial guess on your plant issues is that they may be seeing a deficiency rather than an overdose. To me it is really hard to tell. But the color is a little light, indicating lack of nitrogen. The curling might be a calcium deficiency, or maybe ... ? Hence I am wondering how often you water them. My feeling is that with more waterings, you can (and should) use a lower EC, and you should judge the water quantity and input EC based on runoff EC.
By the way, my pH doesn't change much in runoff. Still 6.0-6.1 usually. I don't measure it much, but I measure EC in almost every runoff.
