Hello I am late to the SPF game and have finally worked out that yes I do need to wear it daily not just when it's sunny. Anyway I have got some and its like liquidy. Do I use this with the vitamin c serum, or use the vitamin c at night? This sounds a bit stupid but the vitamin c says to use with minimum spf 20 and I'm wondering if that's becuase its best to use the vitamin c in the day. I mean it's not protecting my skin from much at night.