Really confused

So i have a 55 gallon tank. I let my tank cycle for 2 weeks and then added live and "dead" rock. I did basic parameter checks everyday and never got a spike of ammonia, nitrite or nitrate. After i added the rocks i started daily water changes while checking the levels but there was still no change in the ammonia, nitrite or nitrate. 0 for all. so yesterday i added 3 damsels thinking they would be ok. (i know it was kinda fast but i figured it would be ok since i haven't had and spikes) 2 of them seem fine and are eating well (i'm feeding them frozen brine shrimp) but the 3rd is dying and i know i'm probably not going to be able to save him.(he hid under the rocks... now i can't find him) I have finally had an ammonia (.50) and nitrate(5.0) spike (nitrite is still 0ppm). My temp is 72.4 and my salinaty is 1.024 and i used the drip method for 4 hrs to acclimate them to the tank.



Is this normal? if not what do i do? how do i get my levels back down? the assistant at the lfs said not to do daily water changes. Thank you and have a great day.