What is happening with my gals?

[OS420]

I'm seeing more and more of these symptoms on the fan leaves of my two, otherwise healthy plants. They are 2nd week in flower and everything seemed fine. Using 600w HPS and they've only been fed once in more than 3 weeks (1st week into flower).
What could be causing this? I want to find the root of the problem to not mess up everything in the most important stage of the plants.
Anyone fancy sharing a similar experience or their opinion?

Edit: forgot to mention, the darkened ends of the leaves first appeared on one of the plants and after a couple of days I some on the other too.

 

[Sumothebully]

If I had to guess, id say the pH in the root zone is too high. What medium are you in?

 

[OS420]

If I had to guess, id say the pH in the root zone is too high. What medium are you in?

I'm using organic soil (I don't remember the brand). I'm not PH-ing my water, I usually use purified water but lately I've only been sticking to tap water.
Though, these plants are ~ 14 weeks old now and they didn't show any of these issues throughout.

 

[BionicKroniK]

I'm using organic soil (I don't remember the brand). I'm not PH-ing my water, I usually use purified water but lately I've only been sticking to tap water.
Though, these plants are ~ 14 weeks old now and they didn't show any of these issues throughout.

Welcome to the FARM and Thanks for Sharing...Nice Job!

What was your reason(s) for changing your water from purified to tap?
Have you ever tested your tap water for any contaminates and/or hardness, etc.?


@ComfortablyNumb

 

[ComfortablyNumb]

Grab a leaf with lots of white spots and flip it over and examine with a microscope or loupe. You are looking for bugs.