Ounces do not equal milliliters

I love my fish. LOVE them. I grew up with an aquarium in the house my entire childhood and have had one the 19 years I've been away from home.

I researched the species, plants, etc. and FINALLY had a great combination in this 75-gallon we bought a year ago. We were just remarking last night how much the fish had grown and how beautiful their colors were.

The only thing I wanted to change was cyanobacteria growing on the glass. Found multiple recommendations for using hydrogen peroxide at a ratio of 1 ml per gallon. Stupid me bought and poured in 75 ounces. Basically, 400 times the dose. I gave all the fish oxygen poisoning. Only one of of probably 30 survived. I took him, a golden wonder killiefish, to Momma's house.

Half drained. Took forever to pull out 75 gallons. 

Below are a few pics of my beauty, several months ago before the plants grew in.

Just sick about it...

 

Now, to start all over again.   :(