A spike in ammonia is going to based on the amount of life on your rock. Sometimes base rock has such a small number of things on it, the bacteria within the rock can pretty much keep up with it and convert it.
I would reduce your lights even more, and slow down on the feeding if you can. If you have a skimmer, you'll need to increase the bubbles or output to compensate for the reduced salinity. It won't perform at its normal setting and so you have to adjust. This wll also help remove some of the stuff your algae loves.
Last thing...make sure to stay on top of your PH readings. It drops to really dangerous levels and must be adjusted.
Good luck man.
