They can be sensitive to water changes. If possible try not to put cold water in during a water change. I have two 55gl barrels that I fill up with water and put a heater in each so that when I do water changes the water temp is the same. I have lost some before when I used cold water. The are a bit more hardy though when bigger.
Also when you get them try and get them all at once and add them at the same time. That is you best bet.
Also when you get them try and get them all at once and add them at the same time. That is you best bet.