HI easydiver
I'm romeo and write from Italy...so excuse me for my probably uncorrect english(I learned at school 20 years ago!)
I've the canon G7 and think that is the same with G9...
I've just bought the IKELITE housing...wondeeeerfuuullll !!! (at today still never dive with the camera inside...)
...but before I dive a lot of times with the camera in original canon housing.
I never use the manual focus because i don't need to do it.
If the water is really murky i don't like to take photos !!( I think that is impossible! )
but if the water is medium murky I can take always MACRO photos using a FOCUS LIGHT in my left hand and lighting the subject directly and precisely (I use the FA&MI 40 watt LED,but I never see this light in my photo...because I have an external flash...)
I think that this is the really solution...remember also,that Canon G7 (and sicurely also G9) can auto-focusing in MACRO mode starting from widest zoom position to 2/3 of the total zoom range(very very wonderful !!!) I never see this in other cameras I had before(nikon coolpix 5400 , sea&sea 8000 G)
hoping that this can help you 


bye from italy 


by romeo