sick goldfish

[g0ldf1sh85]

I have a 36 gal bowfront with 4 goldfish, one angel fish, and 3 cory's. They water changes every 2 days, and always use stress coat. I fed them breakfest and looked at them around dinner time, went back to the tank around 10pm, and 3 of the goldfish were randomly dead and everyone else was coated in a white film. I obviously got all the alive fish out, but have no idea what caused this sudden death. I need help please!

[Brhino]

How big were the goldfish? The tank was either somewhat overstocked or extremely overstocked depending on that question. I'd ask you what your water parameters are, but several dead fish in the tank will create an ammonia spike so it's probably too late to get an accurate reading. How much water were you changing when you did changes? Did you forget to add a decholorinator, maybe? Do you use a heater for the tank and if so was the temperature normal?

[g0ldf1sh85]

there were two 5 in golds, 2 golf ball sized, 1 good sized angel, and 3 small cories. I was doing about 30% water change each time. Yes I added stress coat and stress zyme. Yes, I am using a heater, it has not fluctuated, nothing has changed. I have had the golds for a year, been doing the same thing the whole time.