Tank is struggling and I’m not sure if I’m doing something wrong…

I take care of my bosses aquarium for the day to day upkeep of the tank,but he also hires people to change the water, take care of the electrical side of things and add new stuff to the tank, monitor the chemicals, and they tell us how to take care of them.

I feed the fish the 5 frozen cube food that I let thaw on a plate then just plop in, I clean the filters, and put a seaweed in everyday. Then on Tuesdays and Fridays I give the coral, coral nutrition and put a couple other things in the tank that I don’t know off the top of my head.

The tank has been absolutely taken over by a pest coral and I recently found the little star fish that eat coral on the glass. The people he hires haven’t been super reliable or really been able to fix anything.

Does anyone have any advice? I want to learn how I can take care of the tank better but I don’t know where to start.