Hi shah and welcome to TFF. You'll need to find the marine section of TFF. This beginners section is for Freshwater. I know that in freshwater we sometimes use crushed coral to raise KH and I know that many saltwater tanks actually use this same stuff as the substrate so I would assume it would raise KH in saltwater too but not being a saltwater hobbyist I couldn't tell you for sure! Good luck over there, I know there are a lot of experienced hobbyists over in that section who will answer if you have the patience to wait for them.
~~waterdrop~~