I have had great success with the topsoil made from aged cow manure. It is extremely high in nutrients. I pay $2 for a 40lb bag. I use it in around 75 of my tanks and have not had any noticeable problems.
I buy it at our local Lowes store. It is cow manure that has been composted to the point of it basically being dirt again. Since it is comprised of basically organic material it contains a high nutrient level, which will sustain a planted tank for many years.
I put a thin layer of the topsoil. Then add a layer of rusty nails for iron. Then add about 2" of pea gravel from a local hardware store. Once the plants roots reach the topsoil, you will see a drastic change in your plants growth rates. I have had awesome feedback from many people on the success of this simple setup.
I have used top soil before as my substrate. As far as i know miracle grow doesnt sell top soil, only potting soil. Top soil is the cheapest soil you will find, around 70 Cents for a big bag. I bought mine at home deppot for 70 cents. It looks similar to the color of sand and has no smell, dry and not moist. It is used as land fillers and such. Any organics such as manure, wood chips, and etc will cause a big algae problem in the tank, especially brown algae. Which is why even with top soil, you must mineralize it.
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