Mystery death EBA

So I had a 20 long with 6 giant danios and 4 Eba’s. The EBA that died was purchased a month ago and was 2 -1/2” at death, the other three were put in about a week ago and are 1-1/2”. I feed the danios flakes 2x a day and the eba’s hikari mini gold pellets that have soaked for at least 5 minutes. Water parameters are good as everyone else in the tank seems to be fine this morning. I always gave the big eba more pellets than the little ones but thought it was the right proportions. What killed this guy/girl?