Just can't get it figured out

[Need2grow better]

This is my very first grow it is indoor in soil. I was having problems with the bottom smaller leaves turning yellow and dying off I associated that with them not getting enough light so I upgraded from fluorescent lighting to a thousand watt HPS. The bottom leaves have same to stop dying but I swapped to my 12 12 5 days ago and now some of the tops of my plants seem to be getting a light green to a yellow color. I'm trying to get a couple of pictures uploaded but I don't know if they are going through or not. Any help would be greatly appreciate it and thanks in advance

[Priapus]

We will need some more info first. What nutrients are you using? How often? Strain of weed, Type of soil, size of pot etc

[MonsterEnergy]

those oldest leaves always yellow and drop off, same as the cotyledons
that's just the plants normal process/growth,