It's more than decoration, it's an environment. 

Although mostly used on saltwater tanks, you can use a fake or structured rock for freshwater aquariums. While using fake coral is only appealing eye candy, rock or coral is both very beneficial and a great sight for the eyes. Coral, on the other hand, can be added to the saltwater aquarium once it has finished its Nitrogen Cycle, and the various algae blooms have passed Adequate lighting, frequent water changes, regular maintenance, and stable water parameters will help the coral grow. If you start small, your vision is possible within a few years.

Temp: 78 to 80 degrees 

Salinity: 1.023 to 1.025 SG

Nitrate: <5ppm

Ammonia: 0ppm

Ph: 8.1 to 8.4

It is mostly meant for saltwater tanks, as it raises the Ph levels to the higher side of the scale going above 8. It helps harden the water for the fish that need it and it acts as a filter for them. Two of the best features are that it is your alkaline agent and removes access iron in the tank. Let's not forget the growth effect it has on your fish; it gives your fish such a better environment to grow in.

This rock is a bit harder to handle, it's fragile due to it being clay-like, and it does best in slightly lower than normal Ph levels. (Slightly under 7) As it thrives more so in acidic water, it's meant more so for freshwater low Ph leveled fish. As it develops in the tank, it will need frequent cleanings due to the amount of dirt and debris that get inside the many holes and crevasses. You'll also need to weigh it down to prevent it from shifting as it's very light. Dragon Stone is one of the few stones that you can't stack, but it makes up for it with its presentation.

It's volcanic glass and it doesn't have much of an effect on the Ph levels and it's a great substitute for gravel. Mostly meant for freshwater vivariums, you can also use it on terrariums you can also use it for CAUTION: Dangerous if Swallowed. Sharp Edges, and Fragile. Obsidian is a great way to give your tank an eerie feeling or if you just prefer a darker scene, and you can place it inside your tank after cleaning it thoroughly.

The great quality lava rocks have in aquariums is how they remove nitrates naturally by defusing them as it passes through the tiny holes on the rock. It looks great in tanks, and they stack so well that many comment on how well they stay together and that it's like the rock has glue on it. Though there are many benefits to having lava rock such as: holding plants, providing caves, and lowering nitrate levels. They also have sharp edges that can be removed by grinding 2 rocks together, and the durst and debris from the rocks is a bit of a hassle and water waster because of how thoroughly you have to clean it with water and a brush, that's never been touched by any chemical that isn't specifically for fish, for it to be most effective. After that it is recommended that you boil it for 10 to 15 mins, as they can explode if left to boil for a long time. Although rare events happen where it raises the Ph level, the majority of them shouldn't change a thing.

Petrified Wood is the perfect beginner quartz, to begin with, it is basically fossilized wood, and the stone is formed underground, buried by volcanic ash and other sedimentary rocks. It's durable and has a neutral effect on Ph levels in the tank, though it works best with planted tanks, due to the beneficial iron it holds for plants. Though it may contain toxic minerals, it should be cleared up with a thorough cleaning with a brush that hasn't been tainted with non-fish safe chemicals. It has a very naturalistic look to it, and helps tanks thrive in appearance.