I don't use the decapulated brine. It is an unneeded expense... the bbs are easy enough to hatch with the correct setup. I use a turkey baster and suck up from the pink bottom (actually the top) of the bottle. I have my brine shrimp net positioned over the bbs bottle and put the bbs into that net. I then gently rinse them under the faucet, and upend-swish into a small glass of water. I use the baster to feed these then to the spawns, only useing what they will eat.
My bbs hatching lasts about 3 days, when it is that old I dump it and move the last one I dumped to the front. If you have a new spawn, you should need no more than 1/8 to 1/4 teaspoon of bbs eggs per culture. As they grow you will be using closer to 1/2 teaspoon. Even then you will have a few leftovers, that is ok and better than too few.
The newly hatched ones are better for the smaller fry.
How much to feed? How much can they eat? Start slow and observe.... The small ones won't eat much, when they get larger they eat more.
The first couple days I feed mostly mw, and add a few bbs for those that have the mouth to fit them. Feed sparingly... and closely observe the fry for their eating habits... I am still adding some ocassional mw to my 5 week fry for variety.
The mw will live longer in the tank than the bbs as the bbs live in salt water and the fresh water will soon kill them.