What kind of vitamin C tablets? I don't give my guinea pig any, as long as you give your guinea pigs atleast 2 snacks a day of fresh veggies and fruit and lots of them are high in vitamin C you should be fine. Give them red lettuce with every snack, its really good for them and they love it!

How are they doing? Any luck?

Don't give them the vitamin C tablets in the water, it gives it an 'off' taste and sometimes they will start not drinking it.