Much depends on your overall tank flow and substrate. If you have high flow, sand, and a Watchman Goby digging tunnels everywhere, you typically can't run Fine foam in prefilter stages without quickly clogging the foam. Every system/setup tends to differ. Just be prepared to adjust your mechanical stages with some frequent initial checks of where the waste is being stopped in the path, and don't assume that the manufacturer is putting the best foam in all the right places for you.So should I not use the 60ppi? I have the Fluval G6 and it's prefilter still lets a lot of detritus through, they have the fine pre-filter for marine applications but can't get them for this, they still have the fine for the G4's.
It has been my experience that for some odd and yet unexplained reason, 45 ppi carbon foam does the best overall job as a prefilter in saltwater.