RTN and is tissue loss likely due to a combo of water flow, low alk, inadequate lighting and lack of required nutrients . Increasing flow at this time will simply strip the remaining tissue right off the coral.
I would focus on softies than acros at this time allowing tank to mature and prior to trying acro, I would upgrade lighting, assure there is adequate water flow (no need to blast them) and invest in test kits for at least Calcium, Magnesium and alkalinity.
Take if you can a water sample to a trusted LFS and have them test the listed parameters for you which based on results will give you a clue as to cause and future needs for dosing whether manual or automatic.