It would be interesting to know if the pH of your developer is just over 9.
IDK what is the pH of Gainer's formula but it maybe there is sufficient Borax to buffer it around this value.
Bored yesterday, I waded through a very long thread about Rodinal where Gainer mentions 11.9 as the pH of either his 'rodinal' or that of the person he was speaking with. I'l try and find the recent thread that links to it.
I photograph things to see what things look like photographed.
- Garry Winogrand