Yellowing leaves Week 5 flowering

[mcudogs]

Hi, This is my first grow with 4 Afghan Skunk plants in soil under 400 W led lights. It's now week 5 of flowering and everything was going well with buds growing nicely until I noticed some patchy yellowing of some of the upper leaves on one plant. I've tried comparing it to other problems on this and other sites but can't see anything that looks exactly like it. A second plant is starting to show the same symptoms today.

I am feeding them House and Garden soil at 5ml / litre A and B up to last week and this week I am changing to 3ml / litre.

 

Has anyone any clues on what can be causing this?

[Serrated edge]

What's your ph ?

[Gazza2001au]

I just went thru the same problem not to the same degree as yours but i had the same rusty spots on my leaf's its incorect PH

[oldfark]

You must check ph and ec otherwise your guessing and then these type of things will happen.

Have you flushed or do you use ph balanced water every second or third water depending on your medium?

Get ec meter and ph tester and use them and your troubles will disappear.

Could probably thin out some central vegetation to improve light penetration .

Looks like ph maybe incorrect causing problems with nutrient uptake.

[mcudogs]

I was thinking it was probably pH causing it as last time I measured the pH of my run off it was 5.2. I flushed with 8 litres of pH 7.0 tap water per plant but it only changed the run off pH up to 5.8. How much do I need to flush? I just didn't want to flush them too hard so close to harvest. I also need to understand ec, I've got a meter but need to calibrate it and work out what I'm measuring.

[Faith]

Hiya mcudogs ...Could maybe dilute some dolomite to bring the ph up a bit plus you'll get a cal mag boost a a pretty good time....not tooo sure how fast it can get into the dolo once watered in but can't hurt I wouldn't think? Check it out.  Memory seems to remind me that it is about once tsp dolomite/litrebut it would be wise to research that.  Nice plants

Peace and good gardening to you

Faith

[mcudogs]

Thanks a lot for all of your replies, I am glad I have all of this experience to rely on. I have never really grown anything before so it's a big learning curve. Who would have known growing a weed was so complicated.

 

Only two of the plants are really showing symptoms and getting worse so I gave them both a full flush. I read somewhere you should use 3 times the pot volume to flush so I tried that and at the end the runoff ph was very close to the flush water ph.  I then gave them a feed as well.

 

Hopefully they will survive this and then if all goes well I will flush the other 2.

[hydrochronic]

Looks similar to what is wrong with my plant but not as bad, hope you can sort it out. Will keep an eye on the thread to see how you go.

[mcudogs]

I've flushed all 4 plants now and also gave them a dose of dolomite. The symptoms aren't getting worse any more and the buds are starting to really swell, so i think I'm out of the woods.

Thanks again for everyones help.