I think it's UBS Vita Fresh Vita Gel Shower Filter with 4 Vitamin C Gel Cartridge https://www.amazon.com/dp/B01I4RP7KS/
And the replacement is POSSIBLY UBS Vitamin C Cartridge 5 Pc in 1 Pack for Vita-fresh Shower Filter, 8.82 Ounce https://www.amazon.com/dp/B016I7KQDO/
I wrote possibly is because there are different models, like Vita Fresh or Vita Fresh Gel (Vita-Gel). From my very little research, I got the gel one because it is longer, said to last longer and said to diffuse better. All marketing claims.
I can't attest to them though. I'd say my skin doesn't feel as pulled anymore but that could just be placebo.