My EB Acara died yesterday, and went through the exact same process as yours. My tank has been up and running for 5 years with zero ammonia/nitrites...nitrates were around 40 when it died. Head-standing, then the abdomen began to turn a reddish color. My EB Acara never seemed to tolerate my 40% weekly water changes well and it took it 2 days to recover...which makes me think that a Ph crash was happening. But, my Ph has been a solid 7.6 for years.