Brown spots lower leaves

3 Big Buddha Cheese and 3 Big Buddha Blue Cheese. Started seedlings under T5 in 4inch cups 50% Happy Frog 50% Perlite. These plants are about 4 weeks old from sprouting. Just transplanted them 2 days ago and the tops seem to be growing just fine under 400W MH. Roots looked healthy -although more heavily root bound than I thought. I would have transplanted 1 week sooner. Been watering with purified water - daily - the cups dried very quickly.

At about 3 weeks fed seedlings Botanicare GRO at the seedlings recommendation (7.5ml per gallon). Initially humidity was very low ~30% for the first week or so then I was able to get a humidifier and have been maintaining 40-50% humidity.

Would appreciate any feedback on what this problem appears to be - I have no idea.

thank you !

I see water droplets on the leaves; are you spraying when the lights are on?
That's what it looks like to me. The drops act like a tiny magnifying glass and
burn the leaves. Leaves shouldn't be wet when the lights are on. No big deal
though, they'll be ok.

Oops..I see the humidifier now. I think maybe it's too close to your plants.

Yeah - i had been spraying the leaves fairly regularly with purified water - no nutes -
I am going to stop this. The humidifier is only keeping the tent about about 53% humidity and it does not result in any water or residue on on the plants.

I am going to stop spraying the plants with water.

BUMP - I just got a Hanna combo meter ( calibrated it ) to see what my ph was and I found that the purified water I am using I have a PH of around 6.7.

However I was startled to find that a batch of feeding solution that I made up in a 1 gallon jug ( 1TBSP Botanicare GROW ) - The solution was sitting for about 24 hours and the PH was around 5.1 ? WTF - is it supposed to be that low ? Is this because it sat there for a period of time - should I be using the mix right away ?

Thanks