A Little Advise For A 1st Timer Please!

Hey everybody i just registered with this site today and very excited! i started growing about a month ago and have three very nice plants i believe there all female so fingers are crossed. however i decided to top the oldest of the three around the 5 node and its growing great but the main leaves right were it was topped are starting to turn brown around the veins? i've included some pictures so u can see what im talking about a little clearer. i use 4 100w daylight cfl, 100% organic soil, i used fish fertilizer 10-5-5 to help with the yellow leaves about 1 1/2 weeks ago and i used miracle grow plant food only once 2 weeks a go. i think i doing very well but any comments well help i don't want to miss something or ruin my babies because of my ignorance. thanks everyone

It can be a few things.
Fungi, rust, natural change, phosphorus defiency etc.

It can be naturally occuring colour changes (some strains can have radical colour changes).
It could also be a phosphorus deficiency, this usually leads to leaves crumbling and falling off.
Checking for each possibility is the best way to find the root cause.

I would suggest doing some thorough research of each possibility, compare effects to your own problem and take photos every day to make the diagnosis easier

my vote is a slight phosphorus deficiency, I have noticed the color change tends to coincide with bending and lsting, like when the plant is trying to make a stem move or straining against something, thickening the stem, i think this takes up more phosporus and creates a slight deficiency.

This is just my theory from observing my own plants,

oh and i think it looks a little more maroon/purple than brown, and what kind of plants are those they look pretty nice,

one thing though, if your using miracle grow, or other general soil nutrients alot of the nitrogen comes in the form of urea, which requires bacteria to break it down, I see yellowing on that lower fan leaf and think if you get some great white powder and use just a little in your next watering it will free up some of that nitrogen you have trapped in your soil, ( or so I assume since your using a 10-5-5), or could be a ph issue, I would get some great white regardless, or other mychorizae/beneficial bacteria, grab a bond soil ph/moisture/light reader for 10 bucks off amazon.com, and make sure your watering with and have a soil with a healthy ph.

nevermind i see the brown splotches and I havent seen that before

i think it maybe the rust its more of that type of color plus nitro not being able to be broken down makes sense because i didn't realize that till after i gave it the 10-5-5 but u think that thing off amazon will keep that from spreading? and do u think i should just cut them off like u do the smaller baby leaves?

alright thank u do u think cutting those off would b a better idea? could it spread to the rest of the plant? i think its rust or phosphorus defiency

Do take hasty action unless you are sure.

It's never wise to trim (large) fan leaves as they are a primary light gathering 'device' for the plant.
It's especially bad to trim a younger plant contra an older one, if you feel your plant is overall healty and large enough for such a trim you can try it, but I would not recommend it.

Alter the nutrient solution, make sure the PH is right and let the plant react, before you start cutting your baby.

and i think u burned it a lil buddy. NPK defs appear on more than one set of leaves. dont cut any fan lvs. watch the fertilizer. mj doesn't seem to need much at the stage you are in. half strength...try that first. the affected lvs will turn and fall but not before the plant sucks all the nutes outta it. it's very very easy to give it tooo much NPK when it's a young plant like that. see the chart below. hope you can read it.
dannyboy
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danny may be right burned