Choosing the right substrate is an important part of setting up an aquarium. Different types of substrates serve different purposes and they each have their own advantages and disadvantages. Most substrates provide a surface for nitrifying bacteria to grow on, keeping your aquarium cycled and healthy. It's important to have a layer of substrate on the bottom as glass bottoms can reflect light and irritate or disorientate fish. It also helps make your aquarium look more natural and can provide a surface for aquatic plants to be planted in or root on to.