Photo inclu. What's SUDDENLY wrong with my seedling, YELLOW growth

[MaloMAL]

1 gallon DWC pH @5.8 used poland spring water. No nutrients under a 300 watt viper spectra LED.
Need HELP please i dont understand why it went suddenly yellow

 

[Morth]

Did it have roots coming out of the rockwool before you put it in the dwc?

 

[MaloMAL]

Did it have roots coming out of the rockwool before you put it in the dwc?

Yes it had nice tap root. It currently has a nice colony root. I will send a photo

 

[MaloMAL]

Did it have roots coming out of the rockwool before you put it in the dwc?

 

[AutoNorCal]

It's really hard to see under that light pad just the white balance and repost the image please

 

[MaloMAL]

It's really hard to see under that light pad just the white balance and repost the image please

 

[MaloMAL]

Did it have roots coming out of the rockwool before you put it in the dwc?

I used Rapid Rooter btw

 

[Tupapa]

It looks like a sulfur or iron def., U can add a teaspoon of Epson salt to see if it works