So you're designing a tank and want to know what is the best substrate for a planted tank. Well, the answer is easy... aquasoils! They are going to be the best for plants and here is why.... its all about CEC.
CEC is defined by Perdue University in their research paper Fundamentals of Soil Cation Exchange Capacity (CEC) as "The total number of cations a soil can hold--or its total negative charge--is the soil's cation exchange capacity. The higher the CEC, the higher the negative charge and the more cations that can be held." What this means in our tanks is that the higher the CEC, the more nutrients a substrate will hold on to and make available for our root feeding plants to use. The higher the CEC of a substrate, the more nutrients it can hold. It's really that easy.
There are a handful of options out there for substrates, but none of them can compete with an aquasoil. Sand and gravel are basically inert with a CEC or 0.1-1.3. This means they won't absorb any nutrients so you then have to rely on root tabs which aren't a great option. Seachem Flourite may look nice, but it's also mostly inert even though it's marketed as a planted tank substrate with a CEC or 1.7! The only "close second", which isn't close at all, is EcoCompelte which has a CEC or around 14-16. Aquasoils crush the competition with a CEC or around 45-50! Feel free to reference the chart below.
As we know from Liebigs Law of the Minimum, which we talk about in our "Best Fertilizer for a Planted Tank" video, we want to make sure we are providing more nutrients than the plants need at all times. So it's wise to pair an aquasoils with the EI Method, or an all-in-one like Thrive's All-In-One by Nilogc. These liquid fertilizers will be absorbed by the aquasoil providing nutrients for years to come. It is said in the hobby that aquasoils need to be replaced, but we have seen Fluval Stratum in a tank last up to 5 years and still go strong when paired with a liquid fertilization method. Just make sure you are keeping up on your 50% weekly water changes to make sure no fertilizers or organics build up.
Now not all aquasoils are created equal. Some are pack with more nutrients than others. So the next question is, what aquasoil is the best? The three aquasoils that we really love are int his order: Fluval Stratum, Tropica Aquarium soil and ADA Amazonia. Stratum is a great substrate, but it doesn't seem to come pack with as much nutrients as the other two. ADA Amazonia, version one, has SO much nutrients already in it, that it will literally leach ammonia for weeks cycling your tank without you having to add any ammonia yourself. This can be awesome when starting a new tank. But that comes at a cost as ADA is twice the price of Stratum. But, what if your tank is already cycled and you want to swap an inert substrate out for an aquasoil? Then something like Stratum would be great to use as it still has a high CEC, but just won't leach ammonia. And a good balance of nutrient levels between ADA and Stratum is Tropica's Aquarium Soil. It has more nutrients than Stratum, but less Amazonia, it sits in the middle of the two.
When planting in an aquasoil, just make sure the substrate is 2-3" in depth, at a minimum. You can go deeper if you'd like, but don't go less than 2-3". If you do there is a chance your plant will uproot ruining your design. Just something we wanted to mention.
So keep CEC in mind when designing your tanks. Also, make sure you're doing a complete fertilizer method that the aquasoil can soak up. No sense in having a fancy sponge for a substrate and not load it up with nutrients. Happy scaping everyone!