Some very old articles mention Dr. Rolf Geisler (Germany) also as one of the CO² pioneers. He first mentioned the importance and lak of it of it in planted aqauriums, in a lecture at a Aqaurium Congress in 1965 in Wuppertal Germany.If anyone else discovers earlier references to the use of CO2 in planted aquaria that'd be appreciated too, especially regarding the use of pressurised CO2.
You might be intersted in one of his publications from 1963. A little booklet titled <Aquarium Water Chemistry> still seems to available today via Amazone.
I did never read, so i do not know if CO² is a topic in this book, 2 year earlier than his lecture at Wuppertal.
In 1964 he published a book titled "Wasserkunde für Aquaristische Praxis." I do not know if it was ever translated into English.. If so it would likely be titled "Hydrology for Aquaristic Practice"