Added a lifalili jewel recently to my 90 gallon. Tank is a couple months old and freshly stocked with a jd, gold severum, firemouth, 3 cl, vampire pleco, 4 roseline, and 5 milenniums. All pretty young, no one bigger than 3 inches. Someone is nipping the milenniums - 2 tails are pretty much gone, and one just looks sick... Tank temp at 78, parameters are fine... I haven't witnessed the culprit but had no problems before adding the jewel :/ Advice?