Deficiency or Disease?

Hey all, over the past week the leaves of my plant have started turning yellow with brown spots. I have been ph’ing the water and only feeding light nutes (1/4 strength)...my other 3 plants are going fine and it seems that this “sick” plant is still fattening up the buds, so I’m not sure what’s going on.

I thought maybe it was a K deficiency so I gave a double strength feeding yesterday, but don’t see a difference (might even be a little worse). It started on the lower leaves and spread up. I want to think it’s not disease because my other plants are in the same tent and doing fine, but now I’m freaking out.

Any help would be awesome!!

What are you growing in?
What does "double strength feeding" mean?
What are you doing for Mg and Ca?
And in your last pic, I can see the edge of one of your other plants and it doesn't look fine, so you may want to post full plant pics and give up your details...it'll help someone help you.

Sorry, should’ve been more specific! Growing in Happy Frog, these are White widow autos. Not sure if you can see my post history but I had some nute build up in late veg that seemed to have been fixed after I flushed them, the brown spots are new and seem to be spreading. While the other plants have some yellow, they are improving everyday after the flush. My concern is that the flush wiped them of all the nutes in the soil and they’re starving now.
When I said double the nutes I meant double the quarter strength (so half of what’s recommended). On the most recent feeding I used CalMag - 2mg/gallon, FF Tiger Bloom - 2mg/gallon, FF Big Bloom 7mg/gallon (this is half the recommended dose).
I have dropped some more pics of all 4 plants, this is my very first grow so I know there is quite a bit of opportunity to improve, but I wanted to take them all the way to harvest to really get a grip on the process. A lot of my early mistakes were related to PH/Overwatering/overfeeding nutes, which from the help of this forum I have been able to bounce back from (and learned quite a bit).

There was a point where I was sure these wouldn’t flower, and now they seem to be having a small yield.

It’s pH or over watering. Did you add more perlite to the mix? I currently run this and it’s drainage sucks out of the bag

Sup Im BirDy said:

It’s pH or over watering. Did you add more perlite to the mix? I currently run this and it’s drainage sucks out of the bag

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Not initially, but I top dressed with some 3 weeks ago and it helped. Will definitely be doing 30-40% perlite on the next run. For what it’s worth the pots seem to be drying out pretty quickly every 3-4 days. The runoff PH was 5.8ish which seemed low, so I’ve bumped the water going in to around 7 and that’s brought the runoff to 6.1 which I’m a bit happier with.

If I was you add some dolomite lime to get the ph up and water with ph 6.5. That’s how I got my soil pH up. It will give them Cal/mg but it helped with pH control.

Oh! I forgot to mention that I added some dolo lime (very fine) as a top dressing as well...this was only a few days ago though so I imagine it’ll take some time to bounce back. You think if I get the ph up to 6.5 they’ll bounce back? Why is it that only one of the plants is being hit so hard?
My biggest concern is disease, just want to make sure the really beat up one doesn’t pass anything to the rest...

Sup Im BirDy said:

If I was you add some dolomite lime to get the ph up and water with ph 6.5. That’s how I got my soil pH up. It will give them Cal/mg but it helped with pH control.

Click to expand...

Oh! I forgot to mention that I added some dolo lime (very fine) as a top dressing as well...this was only a few days ago though so I imagine it’ll take some time to bounce back. You think if I get the ph up to 6.5 they’ll bounce back? Why is it that only one of the plants is being hit so hard?
My biggest concern is disease, just want to make sure the really beat up one doesn’t pass anything to the rest...

Parrottroop said:

Oh! I forgot to mention that I added some dolo lime (very fine) as a top dressing as well...this was only a few days ago though so I imagine it’ll take some time to bounce back. You think if I get the ph up to 6.5 they’ll bounce back? Why is it that only one of the plants is being hit so hard?
My biggest concern is disease, just want to make sure the really beat up one doesn’t pass anything to the rest...

Click to expand...

I think it's low pH, causing lockouts. It looks like K deficiency starting on the smaller ones for sure. The big one might be advanced K deficiency or some other nute since it sounds like you've made the soil too acidic.

And in soil, aim for around 6.5 for soil pH.