Crystalline Sulfur (Subnautica)

I’m in the lost river trying to pick up the sulfur for an upgrade. It says to press RT but it just shoots my grappleshot at it. I’m in the toxic goop so I can’t get out.

Where should I place my scanner room for the most crystalline sulfur? Now DONT say the lost river. I know that. But in wich part of the lost river, like ‘the lost river entrance in the bloodkelp trench’ or ‘the cove tree’.