Salinity: 35ppmThis is recession due to stress.
Hammers are intolerant to major swings in water quality, and sensitive to almost any level of copper in the water especially if any tap water was added. Calcium and alk are important parameters that will affect their growth and this coral will start to die off if calcium levels are too low which should be about 400 ppm.
Basically, avoid bright light and water flow and dark lighting. Bright lights cause bleaching and low lighting will cause them to shrink and starve. Maintain moderate light for their photosynthesis and keep it off the sand bed which sand can irritate it.
I suspect your Po4 and Nitrates are elevated and may be causing this - something to check
Temp: 78F
Nitrate: 14.2ppm
Phosphate: 0ppm
Alk: 7.38ppm
Cal: 385ppm
Mag:1380ppm