Jordan, I am curious why you want to breed brine shrimp? I have for a few years, but not as a pet just as food for a reef tank and food for seahorse fry. Are you thinking of making a main display out of them?
I heard they need salt but what kind marine or aquarium??
If you are really serious about growing them to adulthood (around 8-12 days depending on temperature), I think you want to get a good quality salt. Instant Ocean's version is pretty well rounded for this sort of use, Reef Crystals might be a bit high in Calcium. But, BS are pretty hardy so any salt should work. I do not believe the salt used for treating parasites in freshwater fish is adequate, though.
Can i feed Spirulina(powdered) to them?
I use spirulina powder to feed my culture with, looking for the wonderful nutrition that spirulina will provide to my fry. I think you might have better results if you are trying to raise this species with using an algae paste, though. Spirulina is great for enriching the artemia, but not that great for water quality. I find it is hard to work with to get it into suspension. BS are filter feeders, only eating what they capture while they swim with their mouths open, so any food that is not in the water column just deteriorates the water quality.
I use live phytoplankton to grow my cultures in. Water quality stays high, the shrimp grow and reproduce live naupuli every 4 days or so. I have read they live around 3 months and have live naupuli every 4 days?