You are probably right about the water.
Distilled water has nothing at all in it, and that creates osmotic pressure that can and does suck salts right out of your plants.
The only way to use distilled, or RO water is to replace the trace.

Good Hydro nutes contain a little extra Ca and all the trace element.
Soil nutes often do not.

Did a cloning experiment a while back when a vendor started pimping his RO filters here.
He was going on and on about the evils of Chloramine and Chlorine in tap water.
Claimed it was sure death, etc.

So, I took some cutting and set half of them in rainwater, and half in tap water.
No additives.

I watched the too pure water suck those little cuttings dry, then use what they stole to grow bad bugs, (mildew, fungi, bacteria), that finished the cuttings off.
The cuttings protected by the Chloramine and the 120ppm. of "other stuff", rooted and grew jus' fine.
So,my conclusions), a little Chloramine is a good thing, and water can be too pure for our favorite weed.
That said, I have grown some excellent meds that had red petioles all the way through.

Attachment 297478
 I'd say, watch their overall health and don't fret the existing spots, they will not go away, and those leaves are still functioning.
The newest growth is the indicator of their present health.
If the new leaf starts showing spots, we'll put on our thinking cats.
Attachment 297479

And the chart is simple.
Read your PH, find that reading at the top of the chart and draw a line straight down.
If it passes through the fat part of an element all is well.
Through a skinny part?
Not so good.

You will note that Calcium and Phosphorus get "skinny" at about the same PH value.
That is not the best chart for Cannabis, but does serve for diagnosis.

Aloha,
Weeze
Weezard Reviewed by Weezard on . new dude grow new to the scene heres week one https://www.youtube.com/watch?v=n2rUxFLt2co here is week two week two and new UFO - YouTube would love any feedback, pointers or tips.... 3x3x5 with 240 watt full spectrum led and 90 watt red ufo auto sweet coffee ryder, northern lites blue auto, and some auto skunk...cant wait for em to get big Rating: 5