Your parameters, if accurate, do not seem to be worrisome in regards to your issue. Corals without a limestone skeleton do not benefit from high calcium levels to those that need to calcify. 2.5meq/L is in accordance to natural seawater and I have seen much lower with corals still doing well. Consistency is the major factor in husbandry efforts and in your case rapid supplement additions; however, IME this might have more to do with adequate flow. Oftentimes Sarco's will develop spots and/or pits on their tissue followed by a small rationing of brown jelly, which seems to follow suit with what you've documented. This can be especially detrimental during their shed and can even leave holes straight through the tissue. Even though the coral is in a "high-flow" area, sometimes a counter-current flow pattern is needed where the coral is randomly blown from different angles.
At this point, your best bet is to perform a water change, add carbon, and direct flow towards the coral to keep any detritus from settling into the infected area. Don't be afraid to use a toothbrush or turkey baster to remove any brown jelly from the infected area.