Brine shrimp can be fed with the liquid suspension foods sold to marine reef tank owners who have filter feeding inverts, my is called "Liquizell". They are difficult to grow to any size though, and of course, once they're eating, they're producing toxic waste so you need to think about a filter, reef tank grade if you want them to grow to adulthood.
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I used to use an old tank in the garden for free live food - remember to harvest it often - one of the most common things that breeds in these buckets is mosquitos and you don't really want clouds of them emerging from your bushes!!!