How far into flowering did this happen? When plants are blooming/flowering, they pull needed nutrients from the larger fan leaves, which causes them to yellow and fall off. This usually happens at the end of flowering.
If you look at your new growth, it appears a lot darker green than older growth... have you changed anything over the last few weeks? The leaves shouldn't all turn yellow like that, although Sativa's tend to drop a lot of fan leaves prior to finishing. I'd lean towards a nutrient deficiency or nutrient lock, making something unavailable for the plants to absorb, causing the creeping yellowing...I looked closely and thought I saw some of the newer growth's tips getting lighter as well. A Ph of 6.0 is a little low for my preferences, but should be OK unless your meter is off. I wouldn't recommend anything under 6.0 Fox Farms products seem to be high on nutrients, so I don't think that it is a lack of nutrients, but maybe a case of nutrient lock, where the plant can't uptake the needed nutrition.

Are you DWC or Flood n Drain?

Jimster said:

How far into flowering did this happen? When plants are blooming/flowering, they pull needed nutrients from the larger fan leaves, which causes them to yellow and fall off. This usually happens at the end of flowering.
If you look at your new growth, it appears a lot darker green than older growth... have you changed anything over the last few weeks? The leaves shouldn't all turn yellow like that, although Sativa's tend to drop a lot of fan leaves prior to finishing. I'd lean towards a nutrient deficiency or nutrient lock, making something unavailable for the plants to absorb, causing the creeping yellowing...I looked closely and thought I saw some of the newer growth's tips getting lighter as well. A Ph of 6.0 is a little low for my preferences, but should be OK unless your meter is off. I wouldn't recommend anything under 6.0 Fox Farms products seem to be high on nutrients, so I don't think that it is a lack of nutrients, but maybe a case of nutrient lock, where the plant can't uptake the needed nutrition.

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4 weeks into flowering also this is the second run with soil so maybe not enough nutes, doesn't seem like they are eating enough.

chemistry said:

Are you DWC or Flood n Drain?

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Probably more of a flood and drain system...

Yeah once you change to flower nutes there is less nitrogen and thats what you are seeing the plants are pulling nitrogen from the leaves its not uncommon but looks a little much for the time. Depending how far you have to go yet they may benefit from a small bump in nutes.

PureAmazon said:

4 weeks into flowering also this is the second run with soil so maybe not enough nutes, doesn't seem like they are eating enough.

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The devil is in the details. As was mentioned, the plants are using all of their stored nutrients from the fan leaves, but it normally doesn't appear this quickly or massively. The 2nd run of soil makes a huge difference unless you are using the living soil. I've noticed, even with Promix, that a second grow in the soil doesn't produce as big or nice of a yield. With added nutrients, you wouldn't think it should matter much, but t does. The yellowing leaves will probably all fall off soon, but the plant will continue to grow. A small dose of fertilizer would be my recommendation, although most growers tend to go light on nutes towards the end of flowering. You def need Nitrogen, but the yellowed leaves won't recover in all likelihood. I'd give a 1/4 to 1/2 dose of regular nutrients, not special blooming potions or stuff like that. I don't know how much bigger the buds will grow since it depends on a bunch of factors, but you have learned a very valuable lesson regarding using soil multiple times and keeping nutrient levels at the proper levels. It is better to underfeed than overfeed, since overfeeding can kill the plant. Be careful not to add too much nutrients on your next grow.
You should see a difference in new growth color fairly quickly once you give them a snack. Good Luck!!

PureAmazon said:

Leaves are turning yellow and dying can anyone help and tell me what this is. Water is always ph'dView attachment 871580View attachment 871581View attachment 871582View attachment 871583 to 6.0 using fox farms bush doctor coco loco soil. Nutes used general hydroponics flora bloom and floralicious plus. Occasionally will use cal mag plus. 4 days ago used cyco's dr. repair thinking it was an iron deficiency. Thanks in advance.

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You're basically only feeding your plant one of three parts necessary for normal growth, just the bloom is my guess why your plants are showing this issue, assuming your pH is correct

Ive had this happen numerous times over the years, I use Eleanors VF-11 as a foliar spray twice a week and it get new growth back on track fast. Ive been using this for over 25 years as a fertilizer in soil,and also as a bi weekly foliar spray. Done side by side with yields increased by 25% on average.GREAT for yellow and sick plants

Super thrive , easiest product this late and helps revive but as others have said, seems a lack of nitrogen.
I feed veg 1/4 strength along with bloom all the way until flush (3weeks prior) I stop all nutes and let her burn it off and finish.

PureAmazon said:

Probably more of a flood and drain system...

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Is it level? I have a 6 plant flood n drain on the go at the minute, all mainly indica's, but one in the corner is playing up, and I have a suspicion that water on the drain is being left in the said corner, but I'll not be able to comment on that until chop down, then I can lift the plant and give it a good look.