Purple discolouration on leaves, P problem?

So I was checking on my outdoor cannabis plants the other day and noticed some purple discolouration on a few of my plants' leaves. It seems to be most common on the newest leaves that aren't fully developed yet. I did some research and one source online shows a picture of what looks to be exactly what my plants have, indicating that it is phosphorus lockout due to low temperatures. We have been having a colder spell lately where I am but temps don't get lower than around 13 degrees celsius at night. I suspect that the problem could be a result of a soil pH issue which is locking out phosphorus. There is a pear tree next to my spot that drops fruit each year which then rot into the ground. What effect would decomposing pears have on soil pH? hmm... anyways, take a look at the pics. I would greatly appreciate any advice and knowledge my fellow gardeners have to offer!!

if its getting that cold at night, its the weather making the color
13 degree C =55 degrees F

PaulN'Chuck said:

if its getting that cold at night, its the weather making the color
13 degree C =55 degrees F

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I see. I have other plants at a different spot that show no sign of this, though they are much larger in size