I got a quick question

I have sprouts in rockwool. Is purple stems normal? and how soon should I add nutrients? The sprouts are 2 wks old.

Yes, they are normal with certain strains/phenos. The plants will start needing weak nutrients when the 3-bladed leaves start growing in. Seedlings are often transplanted at this point from an inert seed-starter medium to nutritious soil, rather than actually fertilizing them.

if you use a good soil like Ocean Foresdt or Happy Frog you wont have to feed for almost one month.

when you have 3 alternating internodes, it's safe to start feeding at 1/4 strength. at 2 weeks, you should be close if not already ready to feed.