Help - Skunk #1 auto yellowing

[Poooski]

Hi everyone. I am about 4 weeks into my first grow and have learnt a heap from reading these forums.

I have been 2 White Label Skunk #1 in Canna Terra Pro soil under 600w MH and have been feeding exactly as per the attached chart using Biobizz Grow and Biobizz Root Juice. Watering about every 3 - 4 days (I haven't had much run off if any but using about 2l at a time in 18l pots).
The plant I am having problems with is 5 days older than the other one (I had a germination problem) and I have done some LST.
The plant has been growing really well but in the last week I have noticed some yellowing of the bottom leaves. I thought at first these were ones that had been touching the soil due to starting LST too soon but it has slowly spread to most of the plants. The 2 oldest fan leaves are almost entirely yellow. I have also notices a few of the stems going a bit purple.
I have been using a PH soil probe and it has been showing 6.5 in most places but one area was showing 5 today.
Given the PH drop i have just flushed with about 8l of clean water that has been sitting out for 48hrs (all watering has been with tap water that has sat for at least a day).

Keen for any tips - as the second one is looking perfect so don't want it to have any similar problems.
Not sure if I have N deficiency from not enough feeding, or maybe lockout due to too much feeding - or something else.

I cant seem to attach my images but you can see them here



appreciate any help

 

[Poooski]

Here is the schedule I have been using

 

[namvet25]

It's normal for some lower leaves to yellow so just get rid of them.It looks like nitrogen def to me so I need to no the npk numbers of your nutes so we can decide to increase the dose a little.Also,have you used any cal-mag?

 

[Poooski]

Wow, thanks for looking at this so quickly. I have been using bio bizz grow which has an nok of 4-3-6 and also biobizz root juice. I havent used any cal mag. Is it a bit odd that the other one isnt showing any problems?

I have generally been starting the feeding cycle on the day this one sprouted while the other (healthy looking girl) a couple of days later.

 

[Bailey]

I'm with @namvet25 I'm in the same size pots and use the same nutes at that stage I fed 3 ml grow per litre with a fed of 5 ltr and I uzaly get about 200 ml maybe less runoff

 

[namvet25]

It is a little strange that only one is like that.Check your nute bottle and see if it contains any cal-mag and if so what are the numbers.Also you should water so you get some run off to make sure your getting the entire pot watered all the way to the bottom.Don't worry about the purple leaf stems because this is natural with some strains.

 

[Poooski]

I have only been watering about 2l at a time and getting little or no run off. I could have been under watering and hence under feeding. I just put about 8l through to flush anything bad and ordered a new ph tester pen. Ive been using a soil probe to check the soil ph and freaked out because it read 5 at one point - mostly 6 or 6.5 throughout. I need to water the healthy one tomorrow so will aim for a bit more run off. Once the yellow one dries out I'll give her a big water with 3ml grow per L.

 

[Poooski]

Forgot to say the grow nutes dont have any cal mag. I just read a few threads of people saying they get deficiencies about week 3 using biobizz. Any suggestions on cal-mag? I haven't read much on it. Ideally i want to stay organic if i can.

 

[Bailey]

Forgot to say the grow nutes dont have any cal mag. I just read a few threads of people saying they get deficiencies about week 3 using biobizz. Any suggestions on cal-mag? I haven't read much on it. Ideally i want to stay organic if i can.

Black strap molasses has some Cal mag init with is organic eBay has it for £1.99 fed 1 tea spoon per ltr I'm not sure but does biobizz not do algamic with also has cal init

 

[Poooski]

Just ordered some alg-a-mac too. A bit more than £2 but will give it a go. Should be hdre on Friday.
Do you think the yellowing will go away or am i stuck with it? Any thoughts on whether this would have caused a major setback given i am 29 days from sprouting an autoflower? Probably been underfreding for 2 weeks.