make sure to use a good dechlorinator. Also, since your fish are in there taking the brunt of the cycle, and your fish include neons (very susceptible to poor water conditions) the losses are going to happen. To fight this, like Helena said, start with the water changes, and keep this up until your ammonia and nitrite levels are down to 0. Most chemicals like cycle and the like aren't useful, and the only real thing you'll need to be adding to your water is the dechlorinator. Right now the main thing your going to need to do is the water changes every couple of days to combat the ammonia spikes until your filter media has enough beneficial bacteria to remove the ammonia on it's own at a safe rate (cycled).