nutes question

I've heard of a brand of nutrients called Canna. I have Happy Frog soil, and I know they have their own line of nutrients, but I would assume Canna is specifically designed for, well, Canna! Is there any reason to prefer one over the other? Does matching name brand nutes to their soil make any real difference? Which one should I go with? Oh, and here's a pic of one of my green babies! Just giving it plain water with some root enhancer at the moment of course. They're almost 3 weeks old since the seeds cracked. So how much longer till I need nutes? Also, my 400W light is about 3 ft. above them. Do I need to raise them up higher, as they are already in a mylar grow tent? They seem to be loving this Hortilux Blue as is, I don't want to burn them...

Don't be fooled by marketing. Learning the science of cannabis and how it uses nutrients throughout it's life cycle is more critical than having name brand products.
Whats the medium? What kind of light? Personally i'd move it closer-basically raise it 30 centimetres and feel if its too hot for your hand. after about 1 minute if it is; its too hot for your plants.