Northern lights auto first grow when should I use a bloom

Growing Northern lights auto Sensi Seeds there 29 30 days old and am useimg canna a b root juice and call mag was wondering what blooms should I get and when to use this my first grow it’s in coco coir with 600 watt hps

I use grow nutes until she stops stretching. I switch to bloom nutes once stretch is over. Go half strength. If you don't see any burn on the leaf tips increase it gradually. I'm not an expert but I do have a few small grows under my belt and this is what works for me.

I use bloom nutrients for a couple weekly feedings after I see evidence of blooming