To tell the truth, I am not surprised the rest of your fish died, sorry to say...
I had a BIG BIG BIG CO2 overdoes. Just lets say that my KH was AT LEAST 14 and the pH as less than 7, around 6.5. Not good! My CO2 levels were easily over 100, but I only lost 2 fish (a small DD angel and an oto).
All my rasboras made it, I put my "breeder" net in the tank and put the pleco in it so he could get more oxygen towards the top. I also had to support the angels by holding them toward the top with a net.... They would "float" down to the bottom and then lie on their sides, some were even swimming upside down. I saved all but one! You have to be absolutly careful with CO2!
Tank in transition! 55 gallons, hard water.