How deep should substrate be in planted aquarium

How much substrate does your Aquarium need?

How deep should substrate be in planted aquarium

So How much substrate does your Aquarium need? Substrate can be one of the most visual aspects of your aquarium. This alongside plants can really create the most wonderful environment for your coral or fish. The depth of your substrate needs to be understood depending on what substrate and what plants you are using. This has led me to do some research to understand this better and to try and understand how deep substrate should be in a planted aquarium.

Substrate can provide the right conditions for your plants to root nicely and this makes the depth of your substrate very important. The first consideration is to understand how your plants will root. Some aquarium plants are deep rooting whilst others are shallow rooting. The general rule for deep rooted plants is a depth of 3cm to 5cm inches of substrate. You can reduce this to accommodate any shallow rooting plants. Some plants can root without any substrate at all!

What are planted aquarium substrate layers?

Some people like to layer substrate for planted aquariums. This methodology sees a nutrient rich, small in size bottom layer that then is covered with a larger more gravel based top. The reason for the gravel layer is to lock in the nutrients at the lower level as you do not want these to seep in to the main water of the tank.

The risk to layered substrate is that the various layers can get mixed up over time and bring your nutrient rich substrate to the top of the layers and adversely affect your pH levels.

Whether you choose a soil bottom and sand top or a sand bottom and gravel top these types of aquariums do need careful planning and enduring maintenance.

How can I have both deep and shallow rotted plants in my aquarium?

To vary the variety of plants in your aquarium you can use the slanted substrate setup. This is where you will have one area of deeper substrate for your deep rooted plants and a shallower substrate area for the plants that prefer this environment. This can create a very pleasing visual perspective.

Whether you decide to have the deeper layer at the back or to one side, these setups can create a dramatic perspective for your tank. With varying layers of both substrate and plants this is also a very natural habitat for some types of fish too.


What are different types of aquarium substrate?

There are three main substrates to choice from. Gravel tends to be the most popular. This is due to its diversity in color and size but mainly due to it being reasonably priced.

One thing to remember is that substrate can have a direct impact on the pH level in your aquarium. It also plays a part in the filtration of your tank. These two elements are key to plants growth but more importantly to any other occupants you keep in your aquarium.

For plant growth pH of 6.8 through to 7.2 is suggested as the range to promote perfect growing conditions.

Also available are sand and soil. These areas are discussed in more detail below.

What are the most suitable substrates for freshwater aquariums?

As we have just seen pH is a key consideration for your choice of substrate. If you pH is too high your plants will not grow. If your pH is too low you are risking rotten roots which will result in promoting algae growth.

Size of your substrate also needs careful consideration. Gravel that is too small can risk crushing your roots. Conversely gravel that is too large can affect root growth.

Another thing to think about is the colour of your substrate. Light and bright gravels can be over powering for some fish and cause them to want to hide. If you are keeping fish then a darker coloured substrate maybe a more considered choice.

Do I need soil to grow aquarium plants?​​​​

The quick answer to this is no! The majority of pond and sea plants will not need soil to grow. Instead any nutrition required by the plants is generally extracted from the waste generated in your aquarium from uneaten food or waste directly from the fish. Soil can in fact generate additional and unwanted bacteria at the roots of your plants.

However, from my research it appears that plants do grow better in soil. It comes at a price though. Soil substrate is far more technical and difficult to manage in your tank but with time and effort can produce amazing plant growth results.

Aquasoil is a very popular choice in this area. It is dark in colour which means if you are keeping fish this would be a preferred environment for most fish. It can lower pH, which can be a good thing but not ideal for all aquariums. The downside to this soil is that it is very expensive and it can breakdown and degrade over time.

The ADA brand is available in 4 different compounds which include an Amazonian variety. This is actually highly rated if you are growing plants or keeping fish from that part of the world. Creating a plant or fishes most natural habitat will give you the best chance of success. 

ada aqua soil amazonia ii

Is gravel or sand better for an aquarium?

This question seems to split the aquarium keepers community! From the research I have done it is evident that both have their good and bad points.

Gravel is available is many different sizes and colors which makes it very diverse and also more likely to meet your own requirements for your aquarium. Gravel can promote a more solid root structure in your plants. Some plants will actually attach their roots to rocks and gravel so sand would not be a good choice for these plants. For some plants larger sized gravel (almost pebble size) would work very well.

Sand, on the other hand, tends to be much smaller. This causes it to be more dense and compact. The effect on plant roots is that is can cause weak growth and sometime crush roots. Sand is also known for having a more profound effect on pH levels in your water. This will require you to closely monitor pH levels to ensure they remain within tolerance for both your plants and any of your tank’s residents. Sand can also be more easily disrupted. This can cause cloudiness to your water which is not always a desired effect.


Both gravel and sand have both good and bad points so it is worth investing some time to do some research. Your first decision should be based on what plants you wish to use. From this your choice of type of substrate and depth of substrate will be clear.

Final Comments

It all seems a lot to take in doesn’t it?! I have learned so much from surfing the internet and information that is available via aquarist forums. If you do take your time to do your research and make informed decisions then will be best placed to create a spectacular aquarium which will bring hours of pleasure.

The one thing to remember is that you can always start again with completely different types of plant and substrate to give very differing results!