You did the bucket test. You added bleach -- to break down any phosphonates, and then oxidize any metals to the insoluble form, and then soda ash, to raise the pH to the point where they would precipitate.

Colors tell the tale: iron would make the sediment brown or orange; copper blue or green, or maybe black. You got tan. That means calcium plus maybe a tiny bit of iron. You *might* have other metals, but it's unlikely.