Spikes!

For the last 15 days, my tank has read the following:
pH: 7.9
Ammonia: 0-.25ppm
Nitrite: .25-.50ppm
Nitrate: 10-20ppm

Today I added 60 pounds of live rock, I just tested the water (about 10 hours after adding) and my results were the following.
pH: 7.9
Ammonia: 0-.25ppm
Nitrite: 5PPM
Nitrate: over 160PPM

is this normal? This is the first time over ever added live rock to a cycled tank. I got the rock off craigslist and the previous owner said they had been cured and were in storage totes filled with water for a few days... the rocks never got dry, they stayed underwater during the drive home. Is this normal?