as loverotties said it is good for your fish and corals from what i have
read already .
but one thing you shoudl watch for when adding any Vit.C to the tank. your Ph may lower.. it is ascorbic acid. if you are getting Marine C from Kent or anyone else follow the directions fully.
keep in mind a lot of food already has Vit. C in it.
right now i have in front of me..
1.reef prime by ocean nutrition 1,600mg/kg
2.first flake by omgea one listed but no value given
3.Kent Platinum reef herbivore stabized Vit C
4.HBH super soft spirulina pellets listed but no value
5. HBH super soft pellet with krill listed but no value
as you can see most companies already include it in the food for the fish. So adding it to food may not be necessary, adding to the tank for the corals.... not sure.
HTH