Phosphorus deficiency?

[Badfinger]

Problem: What looks to me like rusty water stains

Medium/grow method: Espoma soil

Feed: and supplements used: Dr Earth

water source: ph tap water

Strain/age: FB Blackberry Auto 6 1/2 weeks

light used: 600wat Groplanner

Climate: 79° day. 72° night Humidity 48-52%

Additional info: I'm growing two strains right now. Only my Blackberrys have this issue and its spreading very fast. I did a runoff measurement and got ph of 7.3, but trays are pretty dirty , so not confident that measurement is very accurate. It does not rub off on fingers, so I believe that eliminates a fungus.
I am leaning towards a phosphorus deficiency.
The issue started last week when the flowers started getting their purple undertones. Over night all the large fan leaves starting showing signs of somethings wrong.

I'm thinking phosphorus deficiency, but before I go adding more K, I would like some reassurance, or be stopped from making a big mistake.

When the flowers started getting purple

Fans leaves started looking like this.

This leaf was removed 2 ft from the soil surface, it is NOT nutrient splash.

 

[Drownomatic]

Generally K def starts on older leaves first, from the tips, and leaf margins, so I don't think it's that.

I'm more inclined to think Ca def because of the way its developing in the margins.

 

[Badfinger]

Generally K def starts on older leaves first, from the tips, and leaf margins, so I don't think it's that.

I'm more inclined to think Ca def because of the way its developing in the margins.

Thanks for the reply. I also thought Ca at first. So I gave them a dose of cal-mag 6 days ago, but its still spreading, infact I kind of think it got worse. This particular strain has a big appetite for something. I just don't know what it is.

 

[Drownomatic]

It could also be that Ca is locked out, from high substrate ph.

 

[Badfinger]

It could also be that Ca is locked out, from high substrate ph.

I'm just baffled, everything I put in the pots is ph'd to within 6.2-6.4 ph.
I will have to wash out one of the drip pans before the next watering, in hope's of a more accurate runoff measurement.

 

[hecno]

How well do you know the soil .

 

[Badfinger]

How well do you know the soil .

I would have to say, I do not know my soil. This is my first grow in this brand. But I also don't know my strain. As my issue seems to be strain specific at this time. In my quest to find more info on this strain, the FB site says, light feeder, then to add confusion, in the lower comments section, they tell someone to feed heavy. I personally have been sticking to the Dr Earth feed schedule, which again, is my first time using.
My runoff ph'd at 7.1 last night after watering.

 

[hecno]

Can you probe your soil to see what the Ph is ?

 

[Badfinger]

Can you probe your soil to see what the Ph is ?

I'm getting around 6.7 ph.
I don't know if this is relevant. But in my feeding regiment I had to feed 2 cups of Dr Earth Liquid Gold, not quite a week before the issue started. That stuff took 12-15ml of PhUp. Maybe a ppm overload? Or I did not let my batch sit long enough for a proper Ph measurement?
My AK strain got all the same treatment, and is doing fine, knock on wood.

 

[hecno]

Nothing wrong with 6.7 ph , with out knowing the soil and the nutrients you are using , I would learn to phosphate deficiency , but in saying that how often have you been giving Cal Mag .