There could be many issues... what are your parameters? (List alkalinity, calcium, salinity, magnesium, phosphate, nitrate, and ph, and temperature if you have the test kits). It’s important to keep the parameters in natural salt water ranges, but more importantly is keeping them stable. With such a young tank that is hard, and I had many corals die on me in the beginning stages of my tank, but if you keep everything stable, you should be fine. Additionally, how big is the tank, what is your lighting and flow?