Top leaves discoloration - lighter green spotting

Hi, I read this forum for a while and after starting my last grow decided to join, It has been a good experience so far, going from 4x 150w CFLs to a 430w HPS, the babies are loving it very much.

There has been a problem that has come up recently, maybe you can judge better with pictures, but the leaves are discoloring mostly on the top set of leaves, the ph is between 6.5 and 7.5 I am waiting for a better (digital) tester to help me with this. Not all plants have this symptom and most that have it have it much less (these pictures come from the same plant if I am not mistaken).

They're 3-4 weeks old and are in Scotts potting mix w/ 20% perlite 10% vermiculite and added bat guano 9-3-1 with no other feeding until the 5th nodes are completely showing, then I will start to feed lightly with N (mostly bat guano and a solution that one of my friends will bring).

What could be the problem? Zinc? Mg? N/P/K? Ph problem? I am hoping that adj the ph more precisely will make the problem go away but I have to wait a week until I get my tester.

Something's going on, but this something is nothing. Don't stress; if this is the worst your worst performer is doing then you're on the right track, man. Looking good (enough).

Hey, new development, I have received and plugged my 430w HPS, it was set at 18in of the plant tops but I raised it to 2ft after this morning, I found some bad stuff...

It was plugged in for 6 hrs yesterday and has been running on the regular 18/6 as of today. The plants look a little heat stressed...or I think? Anyways I dunno what to do in this situation. I have two fans, one extracting from the light area and one oscillating over the plants to get their stems mighty strong. The temps are at 100f now with the hps plugged w/ only 1 fan over the plants and the door closed. Ideal temps should be no more than 85f. I am monitoring them to get them lower and will be building an extractor fan which will vent the room to the arctic climate around here (Montreal).

So, heat stress? Or does it indicate something else along with my other post? I am not feeding the plants right now, theyre in Scotts potting mix .07-.01-.03 with added perlite, vermiculite and bat guano (5 tbsp for all 9 plants). I am debating feeding them some guano with the watering that I am going to do later today.