Early yellowing from bottom to mid of plant early in flower(4 weeks)

Hi

I have 3 plants in soil, they are 4 weeks into 12/12 light schedule. One of them is still green and healthy, one of them begins to have yellow leaves but nothing to alarm and one of my plants loose they leaves and have severe yellowing leaves from bottom till middle of the plant.

They are growing in soil mixed with perlite in 18 liter pots, im watering them with tap water that have a PH of 7,i dont know the run off PH cause i dont have a PH meter, no EC or PPM meters as well.
I have feed them with nutrients from Biobizz(biogrow and biobloom), i havent stooped to add the grow nut in flower as i know they need some in stretching stage so i mixed the bloom nut with the minimum dose of grow nut and last week i upped the grow nut in the plant that have this problem with loosing fast her leaves.

From what i can judge its a N deficiency but it seems i cant fix it by rising the levels of N, tip of leaves are already burned a little bit.
Im just afraid that i will loose all my leaves before i can harvest the plant.

Its a 10 weeks flowering plant(Barneys farm LSD)
I attached a picture, can you give me please some advices? What could be wrong? I think Biobizz nutrients has not micronutrients in it as i heard from somebady. Could be some other deficiency other than N?

Im just afraid that i will loose this plant, can she survive another 6 weeks?
Thanks in advance for your help guys

What kind of light?

Everything else looks real good,the yellow leaves don't look like anything to panic about.
Somebody will come along that knows something about them.

Need to get that PH down around 6.5
a lot gets locked out at 7.
a cheap PH meter is better than nothing !
even the test strips they sell for aquariums would help.(UBER cheap)

ive had the same problem, ive been told it cant be fixed that its natural. the green is sucked out of the plant to make crystal of thc. but still 4 week like mine. i tryed cal/mag, ep salts, and nothing worked. but i have to say just go with it and let them dye off. unless someone else can say different.

Re pot, its rootbound and feed and water at 6.5 ph.

iron, sulphur, magnesium, nitrogen and proper PH. You could feed them veg nutrients once or twice.

Additional magnesium along with a moderate amount of N would help them. LSD is a heavy feeder of both. Also have you been feeding them high P bloom foods? If so back off the P...

nameno said:

What kind of light?

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400hps for 4 plants and i will add an additional 250w hps tomorrow

Alexander Supertramp said:

Additional magnesium along with a moderate amount of N would help them. LSD is a heavy feeder of both. Also have you been feeding them high P bloom foods? If so back off the P...

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I will add some epson salt , may i know how much to use it in the water? I used bloom food at half of the maximum strength, N.P.K(2.7.4) I have used it every watering from the start of flowering, is it too much Phosphorus? What damage can do P when over feed the plants with it?