In any case get test kits to test your parameter. Once matching to the required parameters you can add live stock. For skimmer you can get bubble magnus. Adding water for evaporation yes. Changing of water to me is a must as it remove bad stuffs.
it will definitely recover. from my own experience i have a rocks full of red mushroom. water condition is very poor, currently after 3months they recovered and blooming well. (mushroom faded till cannot see. aka melted) and recovers now