Decoding Fluval's Aquasoils: Stratum vs. Bio-Stratum – What's the Difference?

Jan 304 min read

Welcome to the wonderful world of planted aquariums! Creating a thriving underwater garden can be incredibly rewarding, and one of the most crucial elements for success is choosing the right substrate. Aquasoils have become a popular choice for planted tank enthusiasts, and for good reason. Let's dive into why they're so beneficial and then explore the differences between two popular options: Fluval Stratum and Bio-Stratum.

Our Fzone 6G nano with Fluval Stratum — Our Fzone 6G Nano with Fluval Stratum

Why Aquasoils Amazing For Planted Tank's?

Imagine your aquarium plants as tiny humans. Just like us, they need a comfortable place to live and access to essential nutrients to grow strong and healthy. Aquasoils provide both. Unlike inert substrates like gravel or sand, aquasoils are designed to actively contribute to a healthy planted tank environment. Here’s why they're so great:

Nutrient-Rich Foundation: While the misconception is that aquasoils come pre-loaded with all the nutrients your plants need, that's not entirely true. They do have a natural ability to absorb and hold onto nutrients, acting like a pantry for your plants. This is where the magic of Cation Exchange Capacity (CEC) comes in. CEC is like a sponge for nutrients. A higher CEC means the aquasoil can hold onto more nutrients, making them readily available to plant roots. This is why we recommend "charging" your aquasoil with a liquid fertilizer, like our ASG Fertilization kit, to give your plants a boost from the start.
Ideal for Root Growth: Aquasoils typically have a loose, porous structure that allows plant roots to easily penetrate and spread. This is VERY important for carpeting plants, like the dwarf hairgrass you see above. This is essential for healthy growth and nutrient uptake.
Water Chemistry Management: Some aquasoils can help buffer the water's pH, creating a slightly acidic environment that many aquatic plants prefer. We don't recommend you rely on this process entirely, as we think its still important to learn how to test and adjust your water chemistry manually. This will come more into play when the soil is done buffering your water down, but you want to keep it soft. If you need information on how to test and adjust your water chemistry manually, check out the video below.

Fluval Stratum: A Solid Foundation

Fluval Stratum is a widely used aquasoil known for its lightweight, porous structure. It provides a great foundation for plant growth and helps create a healthy environment for beneficial bacteria. It’s a good choice for beginners due to its ease of use. The only downside to it is that it has a larger grain size. This can be ok for larger tanks, as it will not effect the sale of the aquascape, but it can be an issue for smaller tanks, as the granules will look big. Futhermore, larger granules are harder to plant in, as stems can float out of the substrate if you don't have enough in the tank. We teach to have around 2" of aquasoil when installing it into your tank to ensure you have enough soil to hold down more delicate plants.

Bio Stratum: Taking it a Step Further

So, what makes Bio Stratum different? Bio Stratum is essentially Fluval Stratum with added beneficial bacteria, and a smaller grain size. Fluval says that the bacteria they add plays a crucial role in the nitrogen cycle, helping to break down waste and create a balanced ecosystem in your aquarium. This can be particularly beneficial for new tanks, helping to establish biological filtration more quickly. But in our tests, we didn't notice a difference in to the tank cycling quicker, or possibly getting through the diatom phase faster. We also did not see a reduction in cycling when processing a fishless cycle. So we are not really sure what the bacteria is helping. The nice thing is that the grain size is half the size of Stratum, so it DOES help a ton with planting stems, and keeping them down.

Choosing the Right Stratum for You

Both Fluval Stratum and Bio-Stratum are excellent choices for planted tanks as they both have a high CEC, which will allow them to uptake and store nutrients for root feeding plants. We believe Fluval Stratum is more suitable for larger tanks, like 30-40 gallons or more, because its grain size helps keep a larger sense of scale. Where we like Bio-Stratum for smaller scapes, like 2-10 gallons, because it helps keep a smaller sense of scale. Or, if you have an issue with stems or plants floating up on you, Bio-Stratums smaller grain size will help hold the plants down better. Either way, just make sure you have enough to get 2 inches in depth.

Addressing Common Misconceptions

Let's clear up a few things:

Myth: Aquasoils come with all the nutrients plants need. Reality: While they hold nutrients well, you should "charge" them with a liquid fertilizer like our ASG Fertilization kit for optimal growth.
Myth: You can cap aquasoil with sand or gravel. Reality: Capping with other substrates can hinder the aquasoil's ability to exchange nutrients with the water column. So we strongly suggest NOT capping an aquasoil as its not designed to be. You can read our artcile on capping aquasoils here - Should I cap my aquasoil with aquatic sand?
Myth: Aquasoils break down within 12 months. Reality: It takes MANY years for aquasoils to breakdown naturally. Hobbyists used to say that they needed to be replaced every 12 months because they would turn to mush, but we have not experienced that. Furthermore, if the substrate runs out of nutrients, you can just recharge it with liquid fertilizer. What does breakdown an aquasoil prematurally is mixing it with a harder substrate, and the harder substrate grinding down the sofer aquasoil... so just don't mix the substrate with Eco Complete, Flourite, Gravel, anything like that. And be gentle when planting and replanting.