I use nutes on seedlings after they developed the first 2 real leafs. first set of 1 true mairjuana leafs. but i use an organic 0.03-0.002-0.03 no need for mixing, i give them like 25ml with every other watering, till i see the catyledons (or wateva) start yellowing, then i get some actual fert and give them very weak strenght working my way up slowly. if you find weak organic stuff like that and use small amounts theres no way u can burn them, itll just give them a slight boost.