Clark,
What's your current stocking on this tank? It's a Vision tank isn't it? The 180? Give us all the details again and let's work through this step by step. I would simply keep going with water changes, don't panic and don't change anything rapidly until we're sure there's a problem, other than with a dodgy test kit.
Are your fish dying because, as Clive said, if you had 1ppm Ammonia they'd probably be keeling over?
Let's look at this logically. If you're not losing fish; your algae was dying off, the plants were growing and everything seemed fine right? Now on the basis of some test results you seem to be panicking slightly. Are the fish or plants showing signs of trouble or is it just the test kit results you're worrying about?
It's actually pretty hard to kill of filter bacteria. I've had sponge filters that I've kept totally dry and, when they were reimmersed, the filter cycled and I added fish the next day (with very careful feeding) so don't worry too much on that score. Has anything happened to the tank that makes you think they might have died, apart from the test kit results?