First time grow..got problems!

[Apehax]

ok so first time grow!

using a 1.2 x 1.2 x 2.0 grow tent
600 watt hps
using a 6" can fan/6" rhino carbon filter for extraction and a 4" intake, also using a fan inside the tent
temps vary atm because of the weather but on average the temps stay between 77 - 80 light on and 65 on light off

growing 6 dinafem blue cheese feminised auto's (from seed)

they're currently on constant 18/6 from start to finish, they're 18 days old (from shoot) growing in a 'light mix' soil in 6.5ltr pots been watering every 3 - 4 days around 300ml each pot, the pH of the water is around 6.7, i gave them first set of nutes yesterday (plant magic root stimulant + bio grow) ph of soil is around 6.5, i have the hps about 30 inches away from tops of plants

started seeing problems, mainly in one plant, i've read up alot and i can't pin point what it is so here is some pictures, hopefully someone can help me out

 

[Antics]

I can't find any NPK numbers for Plant Magic, and Bio Grow has an NPK of 4-3-6.

How did you mix the nutes?

 

[Apehax]

yeh i found it strange that i can't even see any NPK on the plant magic myself and sorry the name of the other nutes i fed is Bio Harvest Grow and the NPK for that is 9-2-7, i filled a measuring jug upto the 2ltr mark and then followed the instructions on the feed but i halfed what the guidlines told me because they are only young, so i first mixed the plant magic in the water then i mixed the bio harvest grow, then i checked the pH of that water and it was at 6.0, thanks in advance for any help given, i'm new to this and damn it seems so hard haha

 

[Antics]

I would GUESS that the plant magic might be high in phosphorous to promote root growth, as per the product name. But again, I could be wrong too.

how strong did you mix it? or if you could type out the instructions of the ratio they tell you to mix it at, that would be really helpful.

Also, what is the distance from your light to the top of your plants?
What is on the walls of the grow room? Painted? mirrors? foil? etc...

It's hard at first. I went through my first grow just a little while ago, and TECHNICALLY, it was my second grow, because I killed the first two lol. It's a steep learning curve though, and in a short time you'll be saying to yourself 'WTF I know this much already?'

And when you enjoy that first smoke, it makes all the work and waiting worth while.

Oh and welcome to I just noticed you were new here!

 

[Apehax]

hey man thanks for the welcome and taking the time to reply to my post! the light is currently 30" from tops of the plants, its inside a grow tent so the inside is reflective, the ratio of the bio harvest grow is 2 - 4 ml per litre of water and the plant magic root stim says 1.5ml per litre of water, so i filled up 2 litres of water and used a measuring spoon (like for medicine) and used around 1ml of the bio harvest grow and literally a drop on the spoon of the root stim, i dont know wether you can affect the plant with too little, with them being young i figured maybe that would be enough, but its only the lower leaves that show what looks to be nute burn, the newest growth seems fine and the rest of the plants seem fine, but im only learning so i wouldn't know if that looks like a healthy plant or it could die at any moment which i hope doesnt happen lol

 

[Antics]

I'm always happy to help where I can. I was on my first grow myself a few months ago, so I know what it's like, and I know how much you'll know in just a couple months during this first grow. Growing Cannabis has a steep learning curve, so you're going to learn A LOT!

Your soil PH and water PH are perfect. 6-6.8 is best for soil, and 6.5 is optimum. And you're right there.
Growing with HPS I believe the minimum distance for a 600w was either 18" or 24" I forgot which, I'm a CFL grower myself. And your distance is perfect. So it's most likely not a light burn issue either.

Nute burn usually shows burned tips before anything else. The tips of leaves just turn brown and dry.
My first guess would honestly be heat stress. But your temperatures are fine, and the inside of grow tents are designed not to create hotspots like aluminum foil, or glossy white surfaces can create. What about pests? Have you seen any fungus gnats in the grow area, or nearby?

And I'm on the fence between nute burn and deficiency. I can't find anything that looks similar enough to comfortably draw a conclusion yet as to what the problem is.

I'm using these sources:
Cannabis Plant and Pest Problem Solver: Pictorial
Plant Abuse Chart

How are they looking now? We're about 36 hours from when the pictures were taken. How do the spots look compared to before?

 

[Apehax]

ok so, you ask how its progressed its been about 3 days since i posted the pictures, the yellowing has got worse, i've taken more pictures, they're showing pre-flowers but it looks like vertical growth has slowed right down! the leaves are feeling pretty dry but the stems and so on look pretty healthy to me i haven't come across any fungus gnats, that i can see at least an can't see no insects/pests on the plant or anything moving about the soil, i watered last night because the leaves where drooping a bit and the soil felt dry, when i did water it puddled up at top and drained right through like a second later, but when i got home from work this morning they had perked up, i've taken more pics for you as it has progressed but still, nothing on new growth!

here is also a couple of the 'healthier' looking plants and as you can see, i have one in comparrison to the rest thats kinda just shot up lol

 

[Apehax]

could it be that those leaves are naturally just starting to die off, with the full process only lasting 8 - 10 weeks from seed to harvest, went to my local hydroponics shop today and they suggested maybe they actually need food because the light mix soil only had around 2 weeks worth of food and the root stim NPK is 0.14% - 0.03% - 0.12% and 2.3% manganese...so today i bought plant magic soil grow and plant magic soil bloom, but with the preflowers on the plants now, should i just go straight to the bloom feed? bare in mind they are 3 weeks old today one plant at 15" tall and the others vary from 8 - 9" tall but are considerably more bushy than the taller plant

 

[Apehax]

Now at week 7 and this baby smells like hell, think shes almost ready, leaves are starting to yellow now and shes looking ripe!

 

[Antics]

Sorry I missed the update from you before, I don't recall seeing this subscription pop up, or maybe I accidentally closed it..

Either way..
The drooping leaves sounds like a little overwatering. The fact that the water drained into the soil so fast makes me think it was still pretty moist inside, and just the top was dry. You'll need to experiment with your soil mix to determine the best watering schedule.

Some yellowing now is considered normal. But I'd check your PH, make sure it's in the 6.3-6.8 range. If it is, my guess would be low Nitrogen, and it almost looks like a little calcium deficient, and maybe magnesium def. too.

The buds are looking great though, keep up the good work!