Unknown problem

[Brett1980]

I've just run into a problem my leaves on my nl auto are turning a funny colour and even dying I'm 8 weeks into my grow it's been flowering for about 5 to 6 weeks ill post a picture of one of the diseased leaves any help is very appreciated

 

[upinsmoke365]

I would say its most likely either pH imbalance or phosphorus deficiency.

 

[onewarmguy]

Might be two problems, the leaf on the left seems to be showing some nutrient burn, the two to the right seem like an advanced case of thrips. Try cutting your nutrient levels back by 50% for a week or two then check the newer leaves for burnt tips. For thrips spray both sides of the leaves with insecticidal soap or neem oil every two or three days for 10 days. Check this sticky at the top of this forum.
Cannabis Plant and Pest Problem Solver - Pictorial

 

[upinsmoke365]

Might be two problems, the leaf on the left seems to be showing some nutrient burn, the two to the right seem like an advanced case of thrips. Try cutting your nutrient levels back by 50% for a week or two then check the newer leaves for burnt tips. For thrips spray both sides of the leaves with insecticidal soap or neem oil every two or three days for 10 days. Check this sticky at the top of this forum.
Cannabis Plant and Pest Problem Solver - Pictorial

I am unsure its thrips honestly. But I did forget to ask the OP to post full plant pics and not just a leaf. Check out these pictures from below. But it would also help further to know his medium and feed regiment.

 

[Brett1980]

I'll get some pictures in the morning I'm using coco perlite 50/50 nutrients are cyco platinum bloom a and b 3ml per litre of water I then check pH and adjust accordingly to 6/6.5 the plant is nl auto and I'm 97 days into it.
I was thinking phosphorous myself but if that's the case what should I do.

 

[Brett1980]

OK so I tried some extra phosphorous last feed no difference if anything worse.
So I'm thinking someone said mag deficiency I'm going to try that I'll give a little bit at a time it really looks like mag deficiency with the upturned leaves fingers crossed this plant should've been done by now.

 

[Brett1980]

Sorry I probably should have got photos when the lights were off if the pictures don't help I'll get some more tonight at lights out so the hps doesn't turn everything yellow orange

 

[upinsmoke365]

OK so I tried some extra phosphorous last feed no difference if anything worse.
So I'm thinking someone said mag deficiency I'm going to try that I'll give a little bit at a time it really looks like mag deficiency with the upturned leaves fingers crossed this plant should've been done by now.

Looking at the tips of your leafs I am half thinking maybe your overfeeding which can cause lockouts. Also looking at your leaf tips closely, looks almost like nutrient burn. I am growing in coco myself. I personally only feed 1/3 teaspoon Dyna-gro bloom that's roughly 1.6 mil. Then the next day I feed only water just enough to get very little runoff. All PHed to 5.5 to 5.8 ish. Attaching my nutrient values from what I use so you can compare and get a idea.