Ok!
I tried the following:
1. Pressing the CO2 icon to surface instead of the S button on the keyboard.
2. Dived to 60 metres (don't know feet) - saved the game - exit to main menu - loading again - surfacing with the CO2 button
Number 1 didn't solve the CO2 problem for me, but number 2 did.
Just pressing the CO2 icon the sub surfaced and nothing happened to the CO2 levels.
But when using alternative number 2, saving and reloading the problem was solved!
