Well, that is almost definitely what spiked your levels. The rock was probably not cured, and thus, had some die off on it. The die off created ammonia in your tank.
This is definitely not good. I would try to get the ammonia levels down, ASAP. Larger water changes will help. I would also recommend getting a live bacteria supplement, such as Fritz-Zyme's Turbo Start. This will add loads of biological bacteria to your tank to convert ammonia to nitrite to nitrate.
Also, just to give you a bit of advice, both the tang and blenny will need pounds and pounds of more live rock to live. You need another 50 lbs. of live rock in there. Plus, no tangs are really going to live long in a 55.
