The natural way to reduce ammonia is to do frequent water changes. Everyone has different experiences by doing fish-in cycling and/or high ammonia, but with *mine*, the only two fish I lost were both guppies who were sickly to begin with. I'm not sure what was wrong with the first one (he never ate, but he was my first fish and it wasn't until I got another that I realized something was wrong with him), but with the second, he had worms (long stringy white stuff) and I treated him, but it didn't help. You need strong, hardy fish to handle the higher amounts of ammonia.
I take it you have an API ammonia test kit? Watch and test daily.
How long ago did you purchase your fish? There is always the option of returning a few.