First of all, not all mandarins will eat brine shrimp. Most that do only eat the newly hatched brine.
Also, most people hatch bbs, they don't breed them as they have to become adults before they produce liveborn.
For the mandarins, the bbs should be ongrown for about 24 hours after hatchout, and then enriched for two 12 hour stages with new water and enrichment for the second 12 hours stage.
While adult brine can be enriched in a matter of about 4 hours, bbs take a full day for the maximum enrichment, 12 hours for just gut loaded.
It's also safer for the mandarin to decapp or at least sterilize the cysts before hatching as they are known carriers of nasty bacteria.
http://www.angelfire.com/ab/rayjay/Hatcher.html
http://www.angelfire.com/ab/rayjay/brineshrimp.html
When you buy cysts, make sure they have been stored in refrigeration and not kept on shelves or hooks. The quality degrades quickly the longer they are out of refrigeration and is a big reason some people have in failed or poor rates of hatch.