Chances are it never cycled with just the food added. Never got the ammonia up high enuf I'll bet. I'd empty the lava rock, add some base or combination base and live rock and do a fishless cycle. Study our articles senction on cycling a SW tank with shrimp and start over. That's what I'd consider at this point.
If it never cycled, prolly the first thing you added caused ammonia I"m guessing.