While it is logical that a fishless cycle cannot possibly kill fish during cycling, it is perfectly possible to cycle safely with fish, as each of my 3 10g tanks has proven. I have not lost fish to cycling issues, and suspect that your neon deaths could easily be attributed to poor stock, stress in the lfs or en route to the lfs...unless you have taken water chemistry readings that showed ammonia or nitrite levels that were dangerous to fish. Most people would say my 10g tanks are overstocked, with an average of 13 fish in each. With weekly water changes, my levels are 0 ammonia, 0 nitrite and 5-10 nitrate before the water changes! Yet my oldest tank was only started in March and I usually add fish as soon as the temperature has stabilized. However, I do have a lot of live plants in each tank, as well as using Prime conditioner, Stress Coat and ammo-lock in my filter for the first few weeks. I use AquaClear 20's in two of my 3 10 tanks and think it is a very good filter, if filled with decent media.
I am not trying to change your mind, but to set things straight - it IS possible to do a safe fishy cycle if you go about it the right way.
