I have purple afghan doin the same I have three plants going all the same age and only one has red steems so I will be interested in seeing what happens
The blackstar is perfect I think for this set up almost no heat, very quite, I have to wear glasses to look at it is so bright otherwise all I see is green for about an hour. But he just got it 3 days ago so I will keep posting pics and keep you updated.
Ya already planted them in MG before looking into soil too much the organic MG has a 20% mix of perlite in it as well. But going in the fox farm direction for everything