Brine shrimp really don't hold a whole lot of nutritional value, although the fish do love them. A few times a week isn't going to hurt, but like I said, no real value in it, unless you're going to do Live cultures, then there is some benefit.
You can cut the squares up and not have to use up a whole square since you don't need to feed that much.
To feed it, just let it thaw in some tank water and dump it in.
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