Far as what Nitrogen Tropica use? I strongly believe they might be using NH4NO3. The easy way to find out is add few drops of Tropica in the 100 ml water and test it 5 minutes later and see if your test kit detect both NO3 and NH4, if it only detect NH4 then it's highly likely they use Urea.
The good overall ratio of NO3 to urea is if you add 50% N from both, for example: 0.5 N from urea and 0.5 N from NO3, this would add 2.21 NO3 and remaning Nitrogen in Urea form. I also insure I add Nickel in my micro mix to help the urea uptake.