Cycling question ! .......?

The tetras will help to cycle it. However, fish used to cycle tanks often time die very quickly due to the spikes in ammonia and nitrite. If you want to add your fish right away, I would try to get some Tetra Safestart. This supplies the right kind of live nitrifying bacteria to your tank to get it started. I have used this in cycling my aquariums and have had good luck with it. My ammonia spikes were not as bad and did not last as long as they would have if cycled with fish alone, and I'd never encountered any nitrite spikes. Once the ammonia levels dropped I began to show nitrates and my aquariums have been fine ever since. You could also do a fishless cycle by using the Safestart and adding your own pure ammonia into the tank. Keep feeding ammonia into the tank daily and test the water as you would with the fish in it. Add ammonia in the morning and test the water in the afternoon. If it reads zero ammonia in the afternoon and you have no nitrite and are showing nitrate then you are set. But if you are cycling this way, I would change 100% of the water before adding your fish just in case there are any remnants of other chemicals in with the ammonia.