Can it be just genetics, too bright lights, too cold in the long night, or a phosphorus deficiency?

Hello people
Look, I grow 5 White Widow plants and one plant of unknown origin (derived from a regular, non feminized seed of another previous crop of mine, i call it a bastard plant) which suddenly started to show a pigmentation on the leaves, that has turned some leaves purplish brown:







I have to enphazise that this pigmentation isn't happening to all leaves but some of them. This symptom is not seen on any of the White Widow plants, only the bastard plant so far shows this strange coloring of the leaves
This is how the White Widow plants look like:



In this last picture you can see the White Widows look very healthy and beatiful and have all the life in those vibrant green leaves.

I initially thought of a phosphorus deficiency but it doesn't seem the case because they're on their 4th week flowering and a few days before I had started (only for weeks 4 and 5) using a boost fertilizer along with the common bloom fertilizer.

I use the Flower Power brand of fertilizers and pH'd water at 6.5.
Light: DIY led lights ( 3 cree cxb3590; 2 at 3000K and 1 at 5000K) 250W real power from the socket and the grow box is 80 cm x 80 cm x 160 cm. Leds are 15-25 cm from the top of the tallest plants. This bastard plant is a sativa-like plant and it's very long and thin, perhaps for this plants leds are a little closer.
No overfeeding, no overwatering, and I consider the environmental control is fairly good. In the night the temperature may be 10-15 ºC cooler than the temperature during the day (form 5 am to 5 pm the lights are on, temperature 20-25ºC and humidity 50-60%. In the night since we are almost in winter, temperature may drop to 5-10 ºC. Four fans keep on circulating air 24/7. I think the grow box environment is a little warm for the plants during a part of the day but cold in the other, but they'll have to endure, I can't provide them heating for the night. For me is not freezing cold but it may be a little cold for them to feel totally comfortable

What puzzles me is that the Whote Widow have received the exact same treatment as this plant and none of them is showing this coloration of the leaves.
Finally I'd like to say that the leaves don't look sick, they are smooth and firm and fresh, only the color. There are some yellowing leaves but I'd say it's normal to have some yellow leaves by 4th week flowering.
Is it a matter of poor genetics of the bastard plant? Too bright the lights that they are developing anthocyanins? Phosphorus deficiency?
What are your opinions? I'd appreciate your comments. Greetings from Uruguay and good bye!

Gab,
So the obvious question is: Did this strain exhibit that leaf coloration when you grew it before?

Are they all growing in the same bin? Meaning can you change the nutrients for one but not all?

If you gave a bloom boost, it shouldn't need more P. I'm thinking it's just normal strain variation. Like maybe it's a purple strain...

Hey...you growing under the Uruguay legality laws?
JD

@JohnDee thanks for you opinion. I don't know for sure what the traits of the parent plant(s) were, I've no recall from which plant came that seed, I guess I had taken it from those seeds sometimes one finds within buds,like when you grind the weed to smoke, I think it was one of these few solitaire seeds sometimes a given plant produces by herself (or develops it from a pollen grain that came from somewhere and eventually managed to reach the flower). I had grown a few purple strains before (I remember very disappointing crops) but really I can't tell the origins of that seed, but I'm positive it is one of my own seeds, seeds I collect and then I store all together unchecked.
I usually grow feminized seed from known seedbanks. This plant started as a germination experience to my son who chose the seed. Fortunately my son soon abandoned it and then I adopted it. Later as it was growing fine,I decided to give it some of the precious little grow space I have, and put it to flower to see what sex the plant would exhibit, for curiosity.
In fact it is a very beatiful plant, next time I feed her I'll take a full picture.
I give every one of the plants the same nutrients but I prepare the fertilizers&additives solutions individually for each of them, so it is yes, I can chanfge nutrients for one but not all.
When I saw this started to happen, I first thought of an excess phosphorus blocking uptake of some other nutrients (for example cooper and/or zinc). I flushed the roots thoroughly with a lot of pH'ed water and then applied fertilizer solution in very low concentration (1/4 of full strength) and left it alone,
Two days later the coloring has advanced pretty much, and some leaves were almost completely purple brown. What I get from this is that if I was trying a remedy with the last procedure I told some lines above that I did, in fact it seems the remedy has been worse than the malady.
So, I did nothing else from that day and keep on waiting to observe how this situation continues in the next few days.
Regarding to the your last question, I grow marijuana for recreational purpose (and as a hobby I love) wthin the law Nº 19.172/04, I'm registered as a home grower, a lot of people in Uruguay grow cannabis and the other part buys it at the apothecary's shop, supposing there's stock
I'll keep on growing it, it's most of the fun.

Gab,
Well white widows are light feeders compared to many. At lease the WW I grew. So the widows should actually show a deficiency too. But they don't.

You using tap water? Hard or soft? Seems excess calcium blocking other nutrient anion is more likely.

Once it recovers from it's flush observe for nutrient deficiencies. I still feel it's more likely to be strain related.

Good for you guys able to grow legally. I read they were having a little trouble implementing the law but sounds like they overcame that. Legal where I'm at too.
JD

Cold roots will limit P uptake, your roots are getting to cold after lights out at those nighttime temps.