What is your water temp? Keep small bass, under 6" or so in hot water, 85 degrees is good. I would think it is the JD stressing them out but no way to be sure without watching the tank. When that size they need hot water and LOTS of food, they grow fast and once they hit 8" or so they become bullet proof. If your water parameters are what you are saying they are, it has to be related to stress and small bass stress very easily. I would separate them from the JD and try doing a 40% water change twice a week and see if that helps.