Having some problems here..... have a school of medium sized jacks which we cleaned the algae off the sides of the tank and moved around some gravel. Water was replaced with fresh sea water, next morning 1/2 the fish had died and the others looked pretty stressed with lesions on the sides. Did a 50% water change and this morning there were more dead, that looked fine after the h2o change the night before. I'm at a loss as to what has caused this with no prior signs. Any ideas would be apprecated!