It is normal to see a little sand in the sight glass when you backwash.
A CYA level of 200 is not "dangerous" but it does mean that unless you run higher than normal chlorine levels that you will constantly be fighting algae. Take a look at the Best Guess Chlorine Chart in my signature below for more info about that. It also means that you should not be using any forms of stabilized chlorine since they add more CYA. That means no trichlor tabs and no dichlor shock powder.
Hope this helps. Welcome to the Pool Forum!
(By the way, I deleted your other duplicate post. Whenever new members post, their post goes to a moderation queue where it waits to be approved and modded in by one of us. So, although you won't see your posts immediately when you write them, never fear -- they will appear!
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