I have a small-medium size s.a cichlid tank with a pictus catfish and a zig zag eel. I did a water change a week ago and another yesterday. One of my blue acaras died randomly, possibly from stress 2 days ago from my bigger acara since they were both the biggest fish in the tank. And then one of my keyhole cichlids died today, he was acting funny before, but when I got home after getting medicine for him I found him dead, he had red around his pectoral fins. I feed my fish pellets and frozen bloodworms. What could have killed my 2 cichlids so I can prevent it later?