Yellowing bottom leaves 3 weeks into flower

400w HPS cool tube
day temp = mid to high 70's
night temp = high 60's
5 Purple Kush
COCO
Flora series nutrients at full strength as directed on the bottle (flowering stage)
supplementing with Canna PK 13-14 as directed on the bottle
PH = not really sure.... a long time ago I checked the PH of my water with nutes mixed in and it was around 6.5 but Im not sure what the current PH of the COCO is

Problem:

These have been flowering for 3 weeks and Im noticing some of the lower leaves are starting to yellow and brown. Other then the leaves in question the plants look healthy to me...... wondering if these pics tell you guys anything that I could be doing wrong.

Also, as you can see the canopy is pretty dense so not much light is getting through to the lower bud sites is there anything sort of trimming I could do or should I just let them do there thing?

Thanks!

far from enough P in the nutrients. Probably locked due to incorrect pH. Check your pH.

Thats fairly normal, no need for the pk there is enough in the flora and you can lock out N if too much P is present.

Knowing Ph in coco is a MUST! I would veg my plants in coco at 5.8 and when I switched to flower I dropped it to 5.5-5.6 and it came out killer every time. I was also using Canna Coco A and B, cal mag, rhizotonic, cannazyme and would never start out full strength I would at least half the lowest amount on bottle to start out. (rambling )
Your plants look good from the top, older lower leaves will naturally die off. I would say stay the course unless your start seeing signs up top on the canopy of burning or yellowing anything like that. Nice job

Thanks for the input! Im gonna take your advice and cut out the PK 13-14 and half the strength of nutrient solution. Some leaves are showing "the claw".
Next time I think i will be using the Canna coco line I always have troubles when using the flora series.... a nutrient line specially made for coco must be better then a general hydroponic nutrient line especially, since I always grow in coco.

So one more question, how should I go about checking my Ph? Do I just check and adjust the Ph of my watering solution until its around 5.6? can I use any sort of Ph test kit for example one made for a fish tank?

thanks!

its the bud sites drawing the nutes out of the lower leaves you need to either bump up your nutes or check ph and make sure everything is ok also could be salt lockout

it seems it is the ph uve never checked it... u must be mental .... check the runoff and check the water going in it should be going in at 6.3 or any where from 5.9-6.8 the dude u listened to is wrong

Check your Ph daily if in a rez, if you make if fresh daily just check it then. Your gonna wanna catch some of your run off and test that as well, it'll let you know what your coco Ph is, and you can adjust as need be for a watering or two. Yeah I was using a liquid dropper test kit I picked up for like $5 at the hydro shop, I'm sure you could use a pool Ph test kit.
I would def say try the coco nutes, its specifically designed just for it.
And do not listen to dude saying bump the nutes, don't do it!!! Just check that PH!

Not sure if your referring to me, But I had excellent results every grow healthy plants and bountiful harvest, along with what most would call the Smoothest and tastiest smoke they have had in a long time. Who are always asking when there is gonna be more! Wish I coulda shared some with ya.

Thanks again everyone!

sincl9759: Yea, I guess I am mental for not checking PH. Things have been going so smoothly up until now I didn't think it was necessary. Im not gonna bump up the nutes until I know my Ph. One step at a time.

SeanDeerGreen: Thanks for the info on how to correct and check the PH. I have an aquarium so I'll be using that PH test kit. My next watering should be in about 2 days so I'll check it then and report back here once I know!

So, over the past 2 weeks I got around to checking my Ph. Its going in around 6 and run off is around 5.8.
There is no issues with 3 of the plants but 2 of them seem to be suffering (you can see the difference between them in the pics). Smaller bud development, scraggily dropping lover leaves and they don't seem to be sucking up much water! I wanted to see how much water the 2 were sucking up and I ended up waiting 5 days and on the 5th day they were still heavy.....
I'v been switching between full and 50% strength nutrients every watering. I water every 2-3 days on average.
Its going on week 6 of flowering and it would be nice to get the 2 that are suffering healthy again!
got any tips?

Also, One day I was in the garage and I came across an old CO2 tank that I used to use for my other hobby (high tech planted aquariums). The tank is full and Im wondering if it would be worth setting something up in the grow room this late in the game?

heres a few pics.