When to use Neptune's Harvest Fish Fert. 2-4-1??

Ok I went to my local grow store and could only find Neptune's Harvest Fish Fert. 2-4-1 mine are 6 weeks old now, I've used some GH FloraMicro 5-0-1 & GH FloraGro 2-1-6 2 days ago and transplanted them to 5 gal bucks.

When should I use the Neptune, and the only other fert of that brand they had was seaweed, any help?

Thanks Much.