Hi Liliputman, welcome to the forum and thanks for the report! Some comments:
2) Remember actual tank water volume is always less than full tank capacity. In a well planted 100G, I'd take off 10G for substrate, another 5G for plants, and maybe more if there is significant amounts of hardscape. This applies to all chemicals, medications, etc. At 85G, the recommended H2O2 dosage would have been 501ml. Your actual dose was about 25% higher, or 7.4ml/gal.
5) Now this was a surprise. I hadn't considered the time needed to accomplish a water change in a larger tank, and this really slowed full termination of the treatment. Will be giving this some serious thought, I may need to reduce my dosage recommendation to account for variations like this.
What kind of algae was this? Sorry to hear about the two otos, but I'm glad you reported this, and everything else, in such detail.
Life happens. On semi-hiatus, checking in infrequently.