1st Time Grow in BIN - yellowing?

This is my first grow so i'm not sure what to expect...

these plants are all 4 weeks old, 2 are bagseed and the other 2 are from a mate's grow.

I've got them in a bin lined with some reflective mylar type stuff with 2 105 watt CFLs and one smaller 30 watt CFl.

I also chucked a fan in the side of the bin for good measure and added a 'Blaumat JR' to each plant (auto watering)

They'v begun to grow alot faster recently but I've noticed one of the plant's bottom leaves has yellow blotches on it...? Ph? Nute lock up? i dont know.

I water with PH 7 water and am not adding nutes.

Any Help Greatly appreciated!

Attached are 2 pics of my Healthy plant, plus 2 of the set up and one of the sick plant

I cant see the blotches. They look good to me.

Dirtyboy said:

I cant see the blotches. They look good to me.

Click to expand...

i added a better picture of the sick one

ph of 7 is a little high, but passable, try lowering it to 6.7. i know its only a bit but it can make a difference.

the leaves of the other plants are getting blotches on them too....?

So you're watering with PH7, does the soil have any nutes already in it? New sprouts and seedling have enough nutes in their sprout leaves to last what, like 2 weeks? They may be lacking proper nutrition. Any idea what type of soil they're in?

Also whats you're temps like in there

The soil is 'black magic' a type of seedling soil with some ferts in it. I might need to give them some extra nutes but i can't match the blotches up to any known defficiency...

Temps are 23C at Night, 26C during day,
cheers!

Well, 75F on average is pretty good. Do your cups have drain holes in them. Also, whats the NPK on that black magic soil?

yep they have drain holes, the soil didnt come with NPK values but said it contained peat moss and humus.

I'll do a soil Ph and nutrient test now

so i flushed them and am now adding a bit of fert to them , see what happens.

the fert is 12:3:6

Ph in soil is around 7...

I have seen this happen from spraying with the lights on.
Water droplets can magnify under the lights and burn the leaves.

... the leaves (new and old) also have burnt edges (yellow edge-tips). I noticed this before i gave them any fert.