I have a 90 high well planted with 4 angels about 1 yr old, 5 neon 3 rams, 3 cory and algae eaters. When I started out I had 5 giant danios to cycle the tank. They did fine until one day one ended up dead with a bruise on its side. Within a week all five had been killed. No issue with the rams or neons. Replace danios with 3 diamond tetra. Within the last week two have been killed (one had an injury to its doral fin was quarrantined and died) One left. Not sure which fish is aggressive. Most likely angels. Do not understand why as danios were in tank for 5 months and diamond tetra for a month without problems Does anyone have an idea what is going on? (Note rams chase each other)