Thank you all for your kind advice.
I have now put a small cave in the tank to mitigate the presence of the other fish as best as I can until I set up another habitat.
I do currently use ro water with peat to lower the pH however thanks to the advice here I believe I need to become much more diligent in monitoring the water conductivity and overall quality.
I buy my ro water from the LFS. I think I’d better get a conductivity meter and take it with me from now on.