First your carpet looks great!!! I think with a fine grain like you have the challenge will be more of trying not to disturb the substrate. And my experience with Nat Geo sand is that air bubbles attach to it and it floats until the bubble bursts. I know this seems odd to anyone who has not used it before but if its the #5 nat geo sand I experience this every time I change my water as some of the sand from my water fall ends up above the water line and when I fill micro bubble will attach and carry it to the surface. For your first fill I would used aged water (water that has sat for a minimum of 24 hrs.) and maybe add an airstone. This will off gas the water and you won't get all those micro bubble when filling. After that it shouldn't be to much of an issue and as long as you don't disturb the substrate much you should be fine.
Dan
Dan