If you are keeping them in small containers or tubs the water needs to be completely changed everyday. FRT are not as sensitive as many people like to believe. In my experience they are actually very hardy turtles if you provide them with a few simple things (80-85 degree F clean water, varied diet, room to swim and hide). I also keep them together and have never had an aggrssion problem. I've seen many other people keep them together without problems as well. Of course, there will always be individuals that are trouble makers that you must watch for and separate if need be.