Hello again rob...
The point of the "nitrogen cycle" is to grow the bacteria that will eventually use the ammonia and nitrite for food. If you remove large amounts of tank water, you remove these forms of nitrogen the bacteria needs to live and grow. So, if you're starving the bacteria, it can't grow. Make sense?
When you cycle a tank using fish, you choose very hardy fish like female feeder Guppies, White Clouds, Platys, Tiger Barbs or some of the others. These fish don't mind the higher levels of ammonia and nitrite that come from the wastes that dissolve in the tank water. You test the tank water daily and if you have a positive test for ammonia or nitrite, you remove and replace just a quarter of the tank water. This water change gets the water back to a point that's relatively safe for the fish, but leaves enough food for the good bacteria to grow.
You test and change the water for about a month. When several daily tests show no traces of the above forms of nitrogen, your tank is cycled. This means the bacteria has grown to a level that's using all the ammonia and nitrite the fish produce.
Save the large water changes for later when the tank has properly cycled.
Pretty simple.
B
