This article is worth reading: http://www.thekrib.com/Chemistry/ammonia-toxicity.html
In short, your tank is not cycled yet. Adding fish to un-cycled tank is at your discretion as you know the potential outcomes.
When I used the 'original' Amazonia + PS it took 2 weeks of daily 90% water changes to bring the ammonia < 0.5 ppm. I believe that most of NH3 and NO3 is actually coming from PS as it's full of organic mater. When I used Amazonia without PS, I never saw the numbers that high. As the organic matter decays, the pH goes down. I think that's the primary basis of the ADA's claim that their substrates are 'designed' to lower pH. In any established planted tank the pH tends to be lower then the pH of the water out of tap even without CO2 for the exact same reason: decay.