andybutt I tried with guiding dark frames turned on and it actually made guiding worse.
Hmmm, when I tried it, turning on dark frames has not been worse than not turning it on (see my post in this thread from last week).
One thing that you must make sure is that there is no light leak when you cap the guide scope while taking the dark frames, if you don't remove the camera from the guide scope to take the dark frames. You can try testing if light leak is a problem by taking the dark frames with the camera off the guide scope and capped.
ZWO, in pursuit of their "Simple as 1,2,3" slogan, do not give the user the ability to inspect the dark frames.
When I did my guiding dark frames, I simply capped my guide scope (having previously tested against light leaks), but I also covered my guide scope with one of these focusing hoods to further prevent stray lights from reaching the camera: