Natural stone cleaning?

[tino8358]

I bought some cleaner from Monty Miracle to use on this stone. It didnt really work, is there anything that can get the black off this?

 

[ched999uk]

No idea if it's suitable but you can buy 'brick acid' that is used to clean up bricks. Might work on stone - no idea but the manufacturers might know. 

 

[Pjj]

Soft wash it with hypo will come up like new 

 

[Cleanco]

Soft wash it with hypo will come up like new 

I’ve even used hypo on my fence panels to remove algae build up before treating.