I am now setting up a 65 gallon tank with ADA Aquasoil as the substrate. I started with a mix of almost new Africana and Amazonia, then added a large bag of Aquasoil on top. I filled the tank with water and planted a few plants. I measured the ammonia and nitrite in the water for almost 4 weeks. My ammonia peaked at about 3 ppm 6 days after I filled the tank. I started doing 40% water changes about every 3 days. By the 10th day the ammonia level was about .25 ppm, and in 14 days it was virtually zero. At no time did I find my nitrite level above zero. On the 12th day I added many more plants, to what I consider heavily planted - a plant about every 2 inches both left and right and front to back. After the 10th day I did only one 40% water change, on the 19th day, and at no time was the ammonia level as high as .25, probably zero. And, no nitrite ever showed up.
The tank has a Hamburger Mattenfilter, with a lot of biofilter area. I had cleaned it fairly well, by far from very clean, and soaked it in some Excel/water, to make sure no living BBA was on it. I'm guessing that the bacteria still lived in the filter sponge so I had effectively seeded the tank with bacteria, plus the huge amount of plants, primarily about 60 Sag. subulata, was itself a big bacteria source.
Since I can't measure any ammonia in the water, and haven't for the past 10 days, I added 6 otos to the tank today.
I'm not convinced that Aquasoil will always require 6 weeks to stop leaching excessive ammonia. My water is very soft, too, so the pH is certain to be low, making any ammonia present be in the form of ammonium. Otos tend to be very sensitive to water conditions when first added to the tank, so I will soon know how well they are handling the water.