Anyone know why this happens?  My parts are cured and.when I wet sand the resin goes white,  reason I wet sand is the 120 grit tends to leave marks.that can be seen after another coat of resin.

I've no idea about the colour change, but why not use some finer sandpaper after the 120? 120 seems rather fierce for creating a key for the next coat.

It's just what there how too video shows you to you buddy,  but  yeah I think I might try that,  prefer wet sanding but it's clouding the resin :s

If the resin is going white when wet sanding then that is due to the resin not being fully cured before sanding.  Uncured epoxies are hydroscopic until cured so what tends to happen is the moisture makes the resin surface cloudy as it is absorbed. 

I would leave your parts longer to cure to be on the safe side. If that doesn't solve it, have a look at your mixing ratio and batch size to ensure you are within 1% accuracy to ensure things fully cure.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant