Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There are several groups of substrate.
Clay based products such as Oil Dri, Turface, Safe-T-Sorb and kitty litter. The details of each may vary (some fall apart faster than others, some have other issues). In general they can remove the KH from the water, and this allows the pH to drop. Most have high cationic capacity which is good. Means they hold the fertilizers in a way that plants can use them.
Specific plant substrates like Eco Complete and several of the Flourish product line, and others. These may have high CEC, and usually do not raise the GH or KH. Eco Complete made a product several years ago that did increase the water hardness.
Aquarium substrates intended for Rift Lack Cichlids or Marine tanks will almost always raise the GH, KH and pH. Coral sand, Aragonite and others, often limestone based.
ADA products usually remove the KH.
Neutral products not specifically for aquariums: Sands such as pool filter sand and blasting sand. These are graded so all the particles are the same size, and work well in an aquarium. Black Diamond is one brand of blasting sand.
Landscape gravels vary. Often they are shipped all over the USA, but called different things in different areas. The best way to find out about these is to go to your local brick, stone, soils, masonry or similar yards where they sell these materials by the truckload. They will often sell it in bags, too. Take some zip lock bags and a sharpie. Get a handful of whatever gravel or sand you like and label the baggie. Then take those samples home and test them in a glass or jar of water. Whichever do not affect the parameters (GH, KH, pH, TDS) after several days to a week are generally aquarium safe.