possible mg or p defficiency PLEASE HELP!!

Hi, guys so this is my first grow and the plants are huge but now theyre seems to be a problem with one of the newer ones i put in, some leaves are turning brown and curling upwards, not necessarily dying although they might later on. Its concentrated more at the top of the plant at the big fan leaves but symptoms are spreading to lower leaves.

I have been pHing the water only then adding nutes but the other plants dont seem to have a problem and when i did pH the water after i added nutes it still came out acidic(yellow color). I thought it might be chemical buildup so i flushed it twice yesterday. Anyone got any clues as to what it might be and any possible solutions?

I am teaching myself how to diagnose these nutrient issues also and saw someone post this very helpful link (sorry if you've seen it already and its no help):

http://www.marijuana-seeds.net/Thanks-ThankYou.htm

...I understand if its MG def. it's setm will still be green (vs purple or reddish) and you can solve it by adding a tablespoon of epsom salts (99cents at pharmacy or grocery store) to a gallon of water

yea, some stems of the big leave are purple but i think thats on every plant i have, most stems are green so i dont think its phosphorus. How much epsom salt should i put in 1L of water?

My bad, I meant veins, not stems. Well there's about 3.5 L in a gallon so maybe one-two teaspoons to a liter

That's nutrient toxicity, not a deficiency. It looks like there might be some pH damage too.

Flushing was the right idea. You should be pH balancing after mixing your nutrients. If you're in soil you need it at 6.5pH. You should be getting more run off to help this issue.

Thanks for correcting me Snow - do you Ph your water/nute solution or just keep a meter in the soil? I have only managed to get a hold of a soil meter. Thanks.

I pH everything at the end.

Basically, mix in some nutrients. Let it rest. Mix in more nutrients. Let it rest again. Mix in the rest of the nutrients. Rest once more.

pH balance the solution. Allow it to rest 2-10 hours, pH balance again, rest again for 30min to 1 hour. pH balance again if required.

6.5 to 6.7 for soil or 5.8 for hydro.

Spending the $160 on a Hanna combo Gro'Chek pH/EC meter is turning out to be the most valuable piece of equipment in my room aside from the ventilation system and the lighting.

You are a patient gardener. I will take that advice next time I mix up my nutes. Usually I just mix to the schedule and pour then ph test the soil. So far its been okay but i'd rather not take risks if there's better ways about things. Good advice, thank you.