Yellow drying mid-upper leaves, pics

Hey guys, you have been so great in the past helping me out, I decided to ask for some more advice :)

I have two plants, in half gallon soil buckets, under a 400 hps light that just started getting some yellow coloring and a very dry feeling to the mid and upper leaves. They are about two months old. The temp is around 80 degrees in the day and 70 at night. Humidity at 50% on a 18/6 hour light schedule. I have only fertilized them three times so far, and was going to start doing a more steady fertilizing schedule once I start the flowering cycle.

This happened the day after we had to move them from one room to another (temporarily) and then back again. I think it may either be stress from the temporary move or the heat, since before the move, the room was a little smaller and was kept a little cooler.

Its been about two days and the problem hasn't gotten much worse and I would like to start the 12/12 flowering cycle but am not sure if this problem needs to be dealt with first.

Below are some pics and as always, any help is very appreciated.
 

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It looks like a burn. I get those on mine when I put my 400 HPS too close to the girls. It could also be a chemical burn. If it's a chemical burn, just lay off the nutes for a few days and water to flush. If it's the lamp burn then as soon as you pull the light off, it should get better in a few hours.
 
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