[MattKing]

Thank you all for the replies. Indeed I had mixed the whole bottle to working solution (which I agree was probably a mistake). I'll bin it, but could someone first mention why such a tiny amount of fix should ruin the whole bottle, please?

The developer might still function - poorly and inconsistently.

Some developer/fixer mixes can work together as monobaths, but they work in a substantially different manner then when you use the chemicals separately.

And I believe that monobaths need to be mixed up just before use.