I'm guessing it's the well water. You have ppm's but what does the well water start at ? How do you know what's in the well water. I would try R/O or distilled and just some calmag.

We need to know the rez temps too. We just had a cold snap and my bro let the rez temp fall into the 50's and by the next day leaves turn yellow and fell off. I think temps may have gotten lower.

Got to be a diffency. Maybe your well water needs some calmag.