How have you had the tank setup before you introduced your fishes in? Were they all put in at the same time? Any fishes died since Feb?
Even if your tank is cycles, it could happen that you removed too much bacteria, and this is why you would have another ammonia spike and will go through the cycling process again. One of example is replacing all your media inside your filter at once, or rinsing them in tap water.
This image explains nicely how a nitrogen cycle works.