Definitely not twice a week, unless you have a bunch of filtration methods going on, and you have a rather large setup with a lot of water volume. One a week at best, sometimes you don't even need to do it that often.
But yeah, like Corey said, you shouldn't need to feed your LPS
at all. They get most if not all of their nutritional needs from your lights. If you really want to feed them though, just feed them mysis shrimp. Or small chopped up bits of shrimp. LPS
have mouths, and it would be easier for them to eat if you just placed bits of food on their oral discs rather than squirting microscopic food in the tank, which could foul up your water pretty quickly. That's what i did for my zoanthids and my duncan and they all loved it. Marine snow is intended more for filter feeders.