These are two very different types of substrate and you should do your research before purchasing. In this article I’ll go over some main topics such as nutrients, particle size, longevity. Hopefully by the end of this article, you will have an idea of which one best suites you.
In this category, the clear winner is ADA Aquasoil. Although Eco Complete advertises itself as having nutrients, the amount of nutrients will not last that long and will not be capable of growing certain nutrient-hungry plants (such as carpeting plants). But, you can always supplement Eco Complete using root tabs and you probably should if you are planning to grow aquatic plants.
ADA Aquasoil has a mostly uniform size, think of soil rolled into a ball slightly lager than styrofoam balls. Eco Complete is non-uniform in shape and the size will be vary, from the size of large sand to small gravel. They will both hold all aquatic plants as well as the other. You will also find that either substrate will lend itself to having their plants uprooted by fish quite easily, this is due to the large size of the particles. But, as your plants take root, this will become much less of an issue.
It seems that the obvious answer here would be Eco Complete since the price tag itself is far less than ADA Aquasoil. But, you have the consider the relatively inert state of Eco Complete. This would mean that by going with Eco Complete you would have to dose fertilizer right off the bat, so consider that in the price. Where as ADA Aquasoil comes with nutrients that should last at least a year before additional nutrient dosing.
I’ve already covered the caveat of Eco Complete and it’s relatively inert nature. When it comes to ADA Aquasoil you’ve probably already heard of some warnings of its ability to cause a spike in your ammonia levels. What this means for you is, when establishing the ADA Aquasoil you’ll want to do water changes 2-3 times a week for the first 3-4 weeks. During this time, you should not have any livestock but plants should be fine. They do offer a variant that will cause a smaller spike in ammonia but will also be smaller in pellet size.
Also, overtime (2+ years) Aquasoil will tend to lose its pellet shape, essentially turning into plain soil. Eco Complete will not have this issue unless you are purposely breaking down its particles. This means that overtime, Eco Complete will behave the same and require fertilization from the beginning. Where as Aquasoil will not require fertilization for the first year or so and will later require different care since it will reduce to plain dirt.
For something that requires less care in the beginning and is proven to grow plants well right from the get go, I suggest ADA Aquasoil. If you are looking for a budget-friendly answer that may require a bit more maintenance upfront but not too much, then Eco Complete will be your choice.