Fish dying

[TotalDbag]

All of a sudden my fish population has been dropping like leaves (2 died within a week or two). The first one went MIA, and I checked the tank, and didn't find him. The second one I found. She was pretty beat up. I'm not sure if this cannibalism was after she died, or if it's what caused it. She was also a pale whitish color, instead of the normal clear-ish silver color. And I have noticed that my loach has become considerably more active. I replaced the filter cartridge, put some pH, ammonia, etc neutralizer in there. I did just recently change their food diet from Brine shrimp to blood worms, could this be the cause of the chaos? Help me please.