Your tank is looking good. I am guessing from looking at your pics and the fact your losing some corals your Nitrate and Phosphates are high. The reason I say that is, it looks like you have some hair algae growing. I think you said you are using RO/DI water, so I would increase your water changes and cut back on the feeding a little bit and see if you can get rid of the algae. That will help the corals too.