Tattoo discoloration? ?

My friend has a tatoo of a heart on her hand between her pointer finger and thumb. It's black. Had it about 3 weeks. It's starting to lighten up and turn blue. We think it's due to sun exposure abd chlorine considering we practically live at the pool. What do u think is up? How to fix it? And if she gets it done over with more black ink to re darken it will it hurt more or less than the first time?