Nasty leaves on one seedling out of many?

Hey guys! So I have 5 seedlings and 2 clones going right now, and my biggest seedling is showing some odd problems. It started with slowly yellowing lower leaves, but just in the past 2 days I have noticed some spots forming on a couple leaves.

150HPS 24/0
FFOF Soil
veeeeery weak grow big with bottled water

This first pic was taken just a few days ago, the one on the left is the issue plant. Yellowing leaves at this point bot no spotting. That other seedling was planted at the same time (about 2.5-3 weeks ago. The second pic I just took, shows some of hte spotting on the same lower leaf. What's the cause guys!?
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My little cabinet grow. This seedling is the only one with the issue. There are also 2 clones in there
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I'm still learning but those plants look super close to the light. Are they getting enough air? Can you put some distance between those little guys and that big light. They also look kind of wilty like maybe you're over watering them.

Clones need a little time to adjust to the brighter lights if they're under florescent lights first. I usually put mine in a window sill for a day or two and then throw them under the lights.

That's all I've got. Hope it helped some.Good luck figuring it out!

With adequate cooling, a 150w bulb can be about 5" from the plants. Your plants are way too big for plastic cups. Seedlings and clones started in an inert medium need to be transplanted into fertile soil as soon as they are well rooted. Seedlings get repotted when the three-bladed leaves appear.

crying for help becuase my little solo cup is hurting my feet...........I need bigger shoes.

Ehhh I don't think it's the cup because I have clone that I haven't transferred out of it's cup yet. It's about twice the size of this seedling and muuuuch more happy!

They are sitting about 5-6" away from the light, with a peice of lexan seperating them and plenty of airflow. Temps don't get too warm in there.

Here's the other clone I have still in a party cup, but this pic was taken a while ago. It's much bigger now. It will be leaving the party cup soon don't get me wrong

Hmmm I got a PH meter today. The bottles I was using were about 6.8-6.9, and my tap is 5.8-5.9. I know I'm shooting for something in the 6.2 range (give or take), so maybe I'll try mixing the waters and balancing out the PH. Does adding nutes raise or lower the PH?

It's still progressing though, I hope this new watering will help. It actually is on a couple of the seeldings now, seems to be mostly effecting the sativa-dominants.

Alright guys I haven't been able to tackle this yet. I grabbed some vinegar for adjusting the PH, but I'm still getting some nasty seeds. I've been going very light on the vinegar, I'm not sure I trust it yet haha.

It's getting worse on the plant that was first noticed though, the spotting on the leaves has become way more distinct. Almost odd looking to me? Help!

Dude get rid of the solo cup at least get a 2L Bottle Damn hahaha Seriously though you need to repot them ASAP

It's also happening on my clones and bigger seedling in larger pots. I know the cups are going to be a limitation, but they don't seem to be the cause.

Right, But you must realize that the more room and more roots the plant has the quicker it is going to not only grow but heal itself if this happened to be a nute issue it will straiten out in a replant flush situation if it has room for the roots to grow and respond to the problem, Choking them is only going to delay that.