Diana K

Turface will remove the KH from the water. In my tanks it goes from around 5 degrees out of the tap to 0. This also crashes the pH to 6 or lower.
Add some coral sand mixed with the turface, or in a bag in the filter to prevent this.
Turface and Soil Master Select have a very high cationic exchange capacity, so are very good in a planted tank. They tend to be rather light, and do not hold the plants down very well.

3M Colorquartz is a sand-like product that is available in many colors (including black). Google 3M and use their dealer locator. This is a swimming pool product used to give a different color of finish to swimming pools. It is inert, fish and shrimp safe, heavy (easy to clean) but has no significant CEC, so is not so great as a soil. Local swimming pool supply stores and contractors will probably be a good source for this product. It is available in 2 grain sizes.

dawntwister

My favorite sand substrate is river sand. Cost only $3 at landscapers. I use it to cap topsoil.