Not advisable to add nutz in seedling stage. They are quite tender/vulnerable to "burn". What do you have them in currently?
You can, but unless they are in a completly inert medium it shouldnt be needed and will most likely make them worse. It would be better to figure out why they are growing slow. With stunted or slow seedlings, lack of nutrients is rarely the problem.
I have them in canna coco pro plus, but my first lot nearly died they were amnesia Dinafem and strawberry haze, they're just starting to come back but not all. And growing a little funny, I had them under a 300led from china.. Think lights wer dodgy..new seedlings under 300 cfl...still not moving so fast. so i repotted all sh and am into bit bigger pots but the roots had grown all tha way to the bottom and started circling on themselves...man they didn't look healthy at all.