Leaves turning white/yellow, Stems purple. Don't know what to do.

ummm you nuteing? cause someone smarter than me is going to chime in and tell you exactly what deficiencies you appear to have.

Looks like it could be a slight magnesium deficiency. But I'm a soil grower and it looks like thats hydro. I don't know much about hydro.

Adding nutrients? yes.

I have cal-mag, how much should I use?

I dont nute till flower something that many people have different opinions about, but Im like Cereal Box and have only grown in soil so I am out of my league here but to take an adventurous guess you probably have some sort of nutrient deficiency

Yeah, your best bet is to take this to the hydro section. It looks like a magnesium def to me but I honestly couldn't tell you how much to feed with. The guys in the hydro section will know and help you out. Good luck!

Bleached interveins and purple stems=MG def. Ur in hydro. Ask void object he's the hydro mod he knows his shit

Post up some details of your grow situation like type of system, lighting, temps, nutrient schedule, etc...

thank you!

Deep water culture, 600 metal halide, sensi two part grow/bloom. Reservoir is 3 gallons.

What's your pH?

While you are at it, what is the strength of your nutrient solution in the reservoir?