you have to understand that the nitrogen cycle happens in 3 phases...
1. the introduction of ammonia (fish or pure ammonia)
2. the colonization of bacteria that converts ammonia to nitrItes
3. the colonization that converts nitrIte into nitrAte.
So when you cycle your tank you should first get an ammonia reading, with zero nitrIte and zero nitrAte.
Then you will see a slight reduction in ammonia and a readable nitrIte ammount...when the tank is cycled fully you will have a reading of zero ammonia, zero nitrIte and a 20-40 ppm nitrAte...weekly water changes will keep the nitrate in that range.
My advise is to pull the guppies, and do a fishless cycle.
I also have a Magnum 350 on my small tank, and I replaced the carbon with ceramic media.
No matter what you decide to do for fish make sure you get a steady reading of your perameters.
Using Ammonia is not only humane it is more presice of a bio-load and in my opinion one of the fastest ways to get a fully cycled tank.