| | Re: Help with Making MTS
It is frustrating to shop for aquarium soil because there is no standard definition of "top soil" and most products don't list ingredients. Generally, the more expensive soils are more likely to have additives such as peat, compost, manure, and synthetic fertilizer. None of these are desireable for making MTS.
Most natural top soils have less than 20% organic material, the rest is minerals of various sorts. So I agree with DogFish. When I use a highly organic "soil" like Miracle Grow Organic Choice or maybe the Scott's product you list, I like to mix the finished MTS half and half with an inert, high CEC substrate like Turface or laterite.
Read the label on the Scott's stuff carefully if you are considering it. Scott's likes to add synthetic fertilizers to their products, and this would be a bad idea for aquarium use.
"In general, aquatic plants seem to do well in a variety of soils--clays or loam soils with some organic matter. Indeed, I haven't been able to find any major or consistent difference in plant growth in various ordinary soils."
--Diana Walstad, p 132, Ecology of the Planted Aquarium