Aquarium Ornaments

[oxo]

Can anyone suggest what i can use to clean my Fish tank ornaments, they are going black.
Could it be the carbon pad that I have in my filter?

[Buenchico]

This looks as if it might be relevant:
https://www.fishkeeper.co.uk/faq/how-do-i-get-rid-of-black-algae-in-my-aquarium