• Fish make waste in the pond which creates Ammonia. Food also breaks down into Ammonia.
• Naturally occurring bacteria's begin to build as Ammonia is there food source. You can speed this process along by adding that bacteria. That is what is meant by adding Filter Start Microbes or Nitrifying Bacteria.
• These Nitrifying Bacteria reproduce themselves very quickly when the water temperature is above 55 degrees. The bacteria converts the Ammonia into Nitrites.
• While the Nitrifying Bacteria is building so is the Ammonia. You will get a high reading of Ammonia until the Nitrites reach a  high enough level to convert all the Ammonia. At this point you will see a rapid decrease in Ammonia but a high reading in Nitrites. 
• As the Nitrites are building so are other good bacteria's. This next set of bacteria converts the Nitrites into Nitrates. Until the bacteria that converts the Nitrites are high enough the Nitrites will continue to rise. Once enough of the second bacteria is built the Nitrites will drop off to 0 and you will now have Nitrates.

Ammonia can kill fish even at low levels, Nitrites can also harm your fish so you need to keep a watch on them during the cycle process. This process takes 4-6 weeks to complete. Once they are all converted into Nitrates you have less problems but the Nitrates when allowed to get up to very high levels will be food for your algae and therefore promote more algae outbreaks. To combat to high levels of Ammonia and Nitrites during this cycle time the best medicine is partial water changes.