These substrate additives are also sprinkled onto the bottom of the tank before the soil is poured in. They help improve the microbiology or bring in additional nutrients.
Useful bacteria are furthered by some of these substrate additives. These microorganisms help the plants take in nutrients and bring back organic material into the nutrient cycle of the biological system of the tank, thus helping your aquarium plants grow more happily.
Substrate additives provide aquascaped tanks in particular with everything that's vital for aquatic plants, and thus enable the aquascaper to fully concentrate on his or her layout.