my plant's leaves are turning yellow, what is the problem?

I planted my 4 marijuana seeds for the first time about 2 1/2 weeks ago under a 400w HPS light and they were growing fine for the first week or so, until some leaves on the plants started getting yellow from the tip of the leaves towards the stem and the new leaves are not looking too great. the temperature is usually between 81 F and 85 F. I have two fans on them and have the light on 24 hours a day. i'm trying to figure out what the problem is. if any of you have an idea of what it could be please help me.

below are pictures:

are you using Miracle Grow?
you are? over nuted.
You aren't? what is your PH?

They look over watered to me.

those are all factors above AND welcome to RIU! you will find everything you need to know bout weed here at RIU HAPPY GROWIN! Smoke One~

Little Tommy said:

They look over watered to me.

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Since when does over watering cause yellow, not down turned, leaves? Nute burn or ph problem at that age. even heat stress I would think would be a long shot, no?

i reckon it's nute burn too,looks like they either got nute's too early or their is
too much nute's in the soil,you can nearly always tell by the way the leaves riffle and
have more rounded rather than pointy edges!!

Gippy666 said:

i reckon it's nute burn too,looks like they either got nute's too early or their is
too much nute's in the soil,you can nearly always tell by the way the leaves riffle and
have more rounded rather than pointy edges!!

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What kind of Soil you using it looks nute burned to me as well.

nraged said:

What kind of Soil you using it looks nute burned to me as well.

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I'm using a potting mix soil but it also has miracle grow in it. I'm not sure what the ph is though, do you know how I can find that out. How would I be able to fix the nute burn problem

blueinfinity said:

I'm using a potting mix soil but it also has miracle grow in it. I'm not sure what the ph is though, do you know how I can find that out. How would I be able to fix the nute burn problem

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flush the plant plenty of forums and methods on this site to help ya out with the nute issue.! =) as for the ph you can go to your local hardware store and get the liquid tester or the stake tester stake is much more simpler but may be less accurate then doing the liquid one! =) and i know miracle grow soils are on average around a 7-8 ph no bueno for what we are growing here =) i know that my mg was had to control it with up and down organics like viniger and baking soda. well good luck hope this helped happy growing! =) smoke one!!

cowell said:

Since when does over watering cause yellow, not down turned, leaves? Nute burn or ph problem at that age. even heat stress I would think would be a long shot, no?

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yellowing of lower leaves that early can be a sign of the roots not getting oxygen.
heat stress would show in the tops of the uppermost canopy with a hps being the main heat source.

gotta be nutes, ph, or water log.

blueinfinity, how often have you been watering, and have you been letting the soil dry out till dry to the touch? if your water ppm has been properly fluctuating, then you need to flush, and i mean now. use 3 parts water to your soil and run it through. should correct the problem.

surfnugget said:

yellowing of lower leaves that early can be a sign of the roots not getting oxygen.
heat stress would show in the tops of the uppermost canopy with a hps being the main heat source.

gotta be nutes, ph, or water log.

blueinfinity, how often have you been watering, and have you been letting the soil dry out till dry to the touch? if your water ppm has been properly fluctuating, then you need to flush, and i mean now. use 3 parts water to your soil and run it through. should correct the problem.

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I water every 3 days and it usually gets pretty dry on the top. I'm gonna flush it right now. I checked the soil and it has a ph of 7.1 i'm gonna get some powdered sulphur to mix in with the soil to bring the ph level down. if neither of these work I want to try to repot the plants. do you think this is a good idea?
thanks a lot for the help guys