BRIGHT Yellow tops

I am growing some WW and this is the second round. the first went great but now i have 6 clones in a top feed hydro set and the leaves are bright yellow on top. i believe this started when i switched nutrients (humboldt nutrients), though i am not sure. they are about 3-4' below a T5 floro light which is what i use to veg before putting them under a 400w HPS.

Pics are attached, please let me know whats happening here!!

BUMP: My plant is doing the same

you shouldnt be nuting it if its that small bro. idk if thats the problem but it definately aint helping

bump,bump, same here, mine are not that bad but still having the same problem.

What kind of water are you guy using RO, well, rain, tap? Are you using JUST the humbolt? I have not used it myself but the hydro shop says it's the new great thing. I stick with the DM One that I have been using. Also For first timers GH flora series is a great starter nutrient.

I have been having the same problem for a while.
Sulpher deficiency is the usual culprit, add some Epsom Salts (Magnesium Sulphate) although it may take a few weeks to clear up.
I also found backing off the lights a little helps as well.
Are you using any foliar sprays with Penetrator?

Well I'm using rain water,roots soil and my PH is 6.5. and 1000w HPS about 18" away. It suck because I'm 1 week into flowering and this is really slowing things down. The hydroponics guy at the store told me that it was a calcium def. So i dont know.