Why are my leaves yellowing?

The first picture is of one of my 2 white widow girls, yesterday. Yesterday only the bottom leaf was yellowing, though a few of the smaller leaves around the bottom were looking a little brighter green than normal.

Today all of the leaves look to be a lighter shade of green, the lightness moving from the ground up, and the whole plant is lighter than my other white widow (second pic).

I got these plants as clones 4 days ago. At the time they were already about 6" tall (now maybe 8.5"). I transplanted them the day after I got them, 3 days ago, and began tying them down the day after that.

They are in an organic soil mix recommended by the guy who sold me the clones. When I transplanted them (from soil cups, same soil I'm using) I watered them with 4 drops/gallon of Superthrive, and also watered them yesterday, but I didn't really drench the soil, just gave them a little drink. Besides that, I haven't used any nutrients at all.

This plant is sitting under a 250W HPS at a distance of around 2'8". The temperature at this distance is about 82 degrees. Humidity is about 45.

I can't be sure of the PH of the soil or the water I'm using until tomorrow when I can buy a PH meter.

I'm really worried that this yellowing might be spreading to the rest of the plant. Anyone have any tips?

sounds like it needs nutes. I have 7 plants in fox farm happy frog and two in organic soil. The fox farm plants are all way greener and healthier looking. How old is that plant?

I'm not sure how old she is, but she's around 8.5-9" tall (or would be if she wasn't tied). I picked her up as a clone 4 days ago and she was 6.5" when I got her (so how old would that make her?), along with the other WW which was bought at the same time. The guy at the dispensary told me to transplant right away, so I did so the day after I got her.

I have some Fox Farm Grow Big, you think she's old enough for that, and should I star full strength, half strength, or even less?

Also, sorry for the stupid question, but how much water should I water with for a 2-gallon pot of soil? After I transplanted, all I watered each with was 2 red plastic party cups of tap water, and an extra cup the following day.

could be from stress

give it a couple more days and if it doesnt perk up then start worrying