Diagnose this plant please?

[Moonspell]

Strain - Green Love Potion
# of Plants - 1
Grow Type - Soil
Grow Stage - Day 33 from flip
Bucket Size - 2.5 gallon
Lights - 600 Watt HPS
Nutrients - 3-1-2 veg, 2-4 week of flowering 1-5-2, 4-7 week of flowering 1-1-3
Medium - Perlite 25%, soil 73%, dolomite lime 2%
PPM - 1300 @ 4 week of flower
PH - 6.5-7
RH - 50% to 80% at lights off (rainy summer)
Room Temperature - 85 F
Pests - had some catterpillars a week ago, got rid of them

Problem:
Hello folks,
Does this look like phosphorus deficiency ? Or maybe something else ?
Overall yellowing of the leaves appeared around 2 weeks ago, but brown spots are getting more spread around leaves. She was looking a little better yesterday, got flushed, then watered with 1300ppm 1-1-3.

 

[high5]

Hi buddy, I am not quite sure but want to share my experience. When I divert In-Ventilation hose towards directly a particular plant, the leaves' color turns darker and mostly brownish.... I kept doing it to other plants and saw the same result. So my advice is check your inhale ventilation and try to keep plants out of direct air flow.....

 

[Emilya Green]

you have several problems my friend, all pH related. With all the dolomite lime in your soil it is already a high pH environment, but you are also throwing high pH liquids at it... not at all the way to do this.

the goal is to have your soil drift through the usable pH range between every watering. If you watered at the low end of the pH scale, at 6.3, the lime in the soil would cause that pH to drift upwards through the range as the container dried out, allowing the pH drift to pick up all of the nutrients that are needed, each in its turn as its optimum pH level was found.

You on the other hand are watering at the upper range of the pH scale, and not even able to accurately report if you are watering at 6.5 or 7... you give a range. Please understand that 7.0 pH is 50x as base as 6.5... it is a huge difference!

The general yellowing from the bottom could be nutritional... the plants are needing everything right now, especially phosphorus and potassium, and 1300ppm sounds a bit low for weeks 4-6 when you should be throwing the kitchen sink at them, so I would look into increasing your ppm's a bit for the next 2 weeks. Some of the yellowing is also late season fading... your plants are getting older, and they are designed to die at the end of this process, so some of that is normal.

The discoloration at the top of the plant however is very worrisome. It indicates a non-mobile deficiency... usually trace elements, and you have it bad. The nutrients that you need, copper, boron, molybdenum, calcium, magnesium, iron... several others... all have specific pH ranges that they are able to be moved up into the plant... get outside of those ranges and your plant can be sitting in a sea of the stuff, and not be able to use it.

Considering your strong lime content, I suggest adjusting every fluid you give your plants to 6.3 pH... right at the low end of the soil effectiveness. This should allow your plant to pick up the heavy metals that it needs, and then drift up through the range to pick up the macronutrients that you are going to supply a little bit heavier for the next two weeks. I think this will keep your problem from getting worse and messing up your harvest. Here is a chart to explain what I have been saying... pay attention to the soil side of the chart, and always keep in mind that you have added an automatic buffering agent to your soil (dolomite) that will constantly be driving your pH upwards, from the moment that you water.

 

[MadScience]

the purple coloring in the leaves indicates a P deficiency.