Why are my plants yellowing?

[iconsulttt]

I am an inexperienced grower compared to most people on this website. In my 4th year of growing - but I have had good success up to this point.

I am growing outdoors in 7 gallon pots in a greenhouse. My soil is a mix of FFOF + Black Gold + FF Light Warrior + some Perilite. I started my grow on 4/16. I use the Fox Farm Soil Feeding Schedule to the very "T" - I have not varied. I feed every one of the nutrients on the schedule to the plants twice a week. [I had very good success with this last year.]

I just started to notice yellowing on some of the larger fan leaves this week - and now I am getting more. I have compared my leaves with 420 Magazine's Deficiciency and Abundance of Fertilization Elements chart. I am thinking it is a Phosphorus deficiency - but I am not positive. Everything, including water, that I add to the plants is PH balanced to a 6.4-6.7.

Question #1. Is this a Phosphorus deficiency? If not, what is it?
Question #2. How do I correct the problem while continuing to use my Fox Farm feeding regimen? Meaning which of the nutrients do I back off on? Or do I add?

In advance, I thank you for your responses.

 

[vastok]

Your soils are way too hot, one mix not all 3, IMO FFOF is the best even with the dumbest noobs I rec. 25-30% perlite added to that, it reduces the hot soil, prevents root compaction, and allows considerable air into the soil, the wonders of perlite or even river sand.

only in DWC does it really matter what deficiency the plant has, to soil growers its called nute burn!
to handle that you gotta master the flush, in 7 gallons thats an ocean required so................

flush you plants with 3 times the volume of the pot(7 usgall) with ph neutral air temperate water, allow to drain overnite to continue in the morning, no nutes until you see a positive recovery

but the real question has to be asked "Why 7 us gallon pots?" budget 1x us gallon of potting mix per month the plant is with you

please understand, that plants are sentient living creatures (like fish, cat or dog)with their own IQ, etc etc, they will feed when they want, and not to a time table, lol good luck

 

[iconsulttt]

Not questioning any of your answers, but I see that I should have given more information:

Initially I mixed the OF:LW:BG on a 3 to 1 to 1 ratio. And I placed several inches of the Perlite on the bottom of each pot, and added almost an equal amount of the Perlite to the soil mixture.

Mastering the flush. I am not saying I did it correctly, but I did flush the soil for several days before I planted. I just flooded the soil day after day. This was in early April.

The 7 gallon pots are because my grow season is 6-7 months. I did not specify earlier, but my weather/climate is in the Northwest part of the country - Bellingham, WA.


Thank you for your response vastok.