Ok a 3 weels give them a teaspoon or less per gal of water (each, means 1 teaspoon A and 1 teaspoon B)
I havent started mine that young on advanced nutes YET I got it later on in my grow, just like a few weeks ago actually
but this is my intended startup for my seedlings in my 5th grow I have going, so its prob safe.
Also give them a spoon of molasses, blackstarp is best, and a cap of hydrogen peroxide.
Then up the does say a teaspoon or maybe 2, after a month you should be at a table spoon per gal or so.
Im using 1 tablespoon currently, but only on the flowering ones, I dont have any vegging plants so I dont need more than that now.
You can work your dose up just watch, any yellowing tips means nute burn, so stop and only use water next feeding.