Freshwater Aquarium Substrate & Decorations


Substrates and decorations are not necessary in any tank unless the tank has inhabitants that have special requirements. For example, a sand substrate for corydoras because corydoras like to dig and gravel substrates will damage their barbels and even their snouts. If you have a tank of fancy gold fish, discus, or the other types of fish that do not stay on the bottom and do not require any special decorations, there is really not need to place substrate in your tank or decorations in your tank.

Benefit of a Substrate

Substrates are essential for some fish such as sand for corydoras. If you have bottom dwellers such as plecos, substrates will help prevent any type of fungus or bacteria from colonizing onto the bare glass which could cause fungus or bacterial issues for your plecos.

Substrates can beautify a tank and improve its aesthetics. They can provide aesthetically pleasing backgrounds for aquarium pictures. Substrates such as aquasoil can even condition the water, to ensure conditions stay consistent between water changes.

Detriment of substrates

The reason why many hobbyists keep bare tanks is because substrates tend to collect detritus and it makes it harder to perform a tank cleaning with substrate. Substrates make it difficult to fully remove all the fish waste and detritus not picked up by the aquarium filters, increasing the ammonia being produced in the tank.

Types of Substrate


75 gallon aquarium with a sand substrate

Advantages of Sand Substrate

  • Sand substrate can come in multiple shades and provides a more natural look.
  • Pool filter sand is relatively inexpensive.
  • Finer than gravel which means detritus tends to stay on the surface.
  • Finer sand allows for corydoras to sift through it like in nature without hurting their mouths or barbels.

Disadvantages of Sand Substrate

  • Some sand substrates will first leech silica when first used. Silica will cause brown algae to grow, but with regular water changes overtime the silica will finish leeching and the brown algae will go away.
  • Because sand is so fine, it can get sucked into the filter mechanisms and reduce the life of an aquarium filter.
  • Takes longer to prep with rinsing and washing before placing in the aquarium. If the sand is not prepared properly it will cause the water to cloud and take time to settle.

Gravel/Small Stones

Advantages of Gravel Substrate

  • Comes in many shape and colors which allows for any type of choosing.
  • Provides surface area for nitrifying bacteria to grow.

Disadvantages of Gravel Substrate

  • Many of the colors gravel substrate comes in are unnatural.
  • Some gravel can be sharp and can cut bottom dwellers.
  • May wear down bottom feeders barbels and mouths.


Advantages of Aquasoil Substrate

  • Contains key nutrients required for aquarium plants to grow.
  • Usually buffers the aquarium water to a set PH level.
  • Looks good and comes in a variety of colors.

Disadvantages of Aquasoil Substrate

  • Aquasoil is more expensive than sand and gravel substrates.
  • Breaks down over time resulting in the loss of shape and messiness when water changing and cleaning the tank.
  • Leeches ammonia into the water for up to a month which means it requires special preparation before any fish or shrimp can be added into the tank.

Garden Soil

Garden soil is generally used for aquascaping and planted tanks as a cheap alternative to aquasoil. Like plants that grow on land, some aquarium plants have roots that borrow into the substrate and absorb nutrients. By using a first layer of garden soil and covering it with a heavy substrate that will not allow the soil to leech into the water, the aquarium plants will be able to absorb the nutrients in the soil without allowing the soil to leech into the water.

Advantages of Garden Soil

  • Much cheaper than aquasoil.
  • Contains nutrients required for aquarium plants to grow.

Disadvantages of Garden Soil

  • Needs to be covered with other substrate to prevent the soil from clouding up the water.
  • If left uncovered, will cloud up the water. Being disturbed when uncovered will cause the water to get clouded.


Decorations are not necessary unless some of the aquarium's inhabitants have special requirements. For example, the natural environment for most species of plecos is at the bottom of fast flowing rivers. In these rivers, the bottom of the river is full of river rocks that form natural caves and driftwood that also forms caves. Plecos have evolved to claim caves for general habitation and for breeding. Panaque plecos have evolved to survive on driftwood.

The natural environment for cichlids are large rocks and sand. Certain types of Cichlids use rocks for food, habitation, and breeding. Therefore it is important that a cichlid tank contains the same elements placed in such a way as to provide hiding spaces and breeding spaces for cichlids.


In nature, many fish seek shelter in cave like structures. Caves can provide security and a place to reproduce. If the aquarium has plecos or cichlids, caves will provide them with the security to feel safe in the aquarium. Feeling safe allows these types of fish to feel comfortable enough to be out in the open.


Rocks are naturally occurring in a lot of the environments aquarium fish are found in. Again, for bottom dwelling type of fish and cichlids, rocks are important for the feeling of safety and providing the fish a place to hide.

Natural rocks provide your aquarium with aesthetics of naturalness.

How to Determine if a Rock is Safe for your Aquarium?

If there are naturally occurring rocks around where you live, you may be tempted to use those rocks in your aquarium. You'll want to follow a few precautions first before doing so, as the rocks may contain minerals or chemicals that could change your water parameters or could cause your fish to die.

Test the Hardness of the Rock

  1. First test to perform is to test the hardness of the rock you are considering.
  2. Use a steel object such as a steel knife to scrape the rock you are considering.
  3. If a mark shows up on the rock, you know the rock is softer than the knife and its probably
  4. If the knife doesn't leave a mark on the rock, it is probably safe for your aquarium.

Testing for Carbonate Hardness (The Acid Test)

The purpose of this test is to test for carbonates and bicarbonates in the rock. The reason we want to test for carbonates and bicarbonates is because if they are present they will buffer the pH of the water to roughly 8 to 8.3.

  1. You can use vinegar to perform this test, although a stronger acid is preferable. A stronger acid will be able to test weaker carbonate levels. Common acids to use are muriatic acid or the API Master Test Kit Nitrate Bottle 1.
  2. Use a few drops of the acid on the rock you are considering.
  3. If the drops start to fizz, there is carbonates or bicarbonates in the rocks that will buffer the pH of the water.
  4. Carbonates are not necessarily bad for the water as some fish prefer high pH levels.

Study the Rock for Metals

  1. Review the rocks you have chosen for any type of flaking and any sign of mineral deposits in the rocks.
  2. Mineral deposits could leech into the tank water changing its parameters or potentially harming fish.

Because of the potential to change water parameters or harm the aquarium's inhabitants, if there is ever any doubt about a particular rock, it would be best not to include it in the aquarium and to choose other rocks. With the effort that goes into aquascaping, it would be devastating to place a rock that could destroy your efforts.

Aquarium Decorations

20 Gallon Aquarium with java moss, fake pink floating plants, and a sand substrate

Various unnatural looking aquarium decorations could allow an aquarium hobbyist to personalize and inject their style into their aquarium. These decorations can further benefit the fish by providing hiding spots and increasing their security in the tank. They can provide aesthetically pleasing focal points for observers of the aquarium.

Real Plants

Real plants provide hiding spots for fish, break up line of sight in a tank which is useful for territorial fish, and absorb nitrates from the aquarium. A downside to plants is their maintenance, and the fertilizers and substrates they require. If your focus is on the fish, attempting to keep plants alive or to find out why they aren't doing well could detract from the enjoyment of watching and caring for the aquarium's inhabitants.

Fake Plants

Fake plants provide the same benefits as real plants by providing hiding spots for fish and in some cases a place for spawning fish to attach their eggs to. Furthermore, some fake plants are so well made that they end up looking as good or better than their real counterparts. Another benefit of fake plants is that you do not have to worry about having the correct substrate for their growth or maintenance of the plant.