All dead?

i was wondering if anyone had heard of a problem with ocean nutrition flakes or pellets? I bought a container of each the other night, fed my fish (which is what they have been eating for the last year) and the next day when I got home from work, all three of my fish were dead. I don't know how long they had been dead, but they were at the bottom of the tank very much not alive. That is the only thing I can think of that would have caused all three of them to die in such a short amount of time along with my scarlet cleaner. My anemones are still alive though they were unhappy with the new water quality, my snails are all alive, and my hermits are still good. I have also discovered how many bristleworms I have (side note: they really give me the willies) because they have been coming out more recently. Not sure if this has to do with whatever problem I have with what killed the fish. I didn't check water parameters because I figured with three dead fish, it's likely to be slightly skewed. But, my salinity has been at 1.026 which is where I have always kept it, and the water temp has been a balmy 78 degrees. If anyone has any ideas please let me know! I'm completely stumped as to what else it would be seeing as it's just the fish and shrimp! No signs from my anemones or anything else that anything was wrong such as chemical warfare. And the "all of a sudden" aspect... i'm lost. And heartbroken. 

Nitrites and ammonia are at 0, ph is about 7.8, and nitrates are at about 5. No soap was anywhere near the food or my fingers, nothing has been added within the last month accept a new canister filter which had been switched out about 3 weeks before this happened. There is no stray voltage that I have found, and I have been feeding the same amount of food to the fish for the last year. This is why I am so baffled as to what the crap happened! I haven't changed anything I have been doing and randomly they are all dead at the same time without affecting my anemones or my clean up crew. Nitrates are a little high I know but when i first started they would get way worse (prior to a protein skimmer) and nothing like this happened. At that point I also had 5 fish in the tank instead of just three. I'm afraid to go out and restock until I know what happened. Thank you for the sympathies and suggestions. I appreciate everyone's help.