Best Acid cleaner for Sandstone?

[Mike13]

Hi, got quite a bit of sandstone that has been down a little while now, want to freshen it up and remove the rust washed in from soil walked over it.
I have used a diluted acid cleaner and it doesnt damage the stones ( I washed it off quite quickly to be sure)
What is a good cost effective cleaner to buy? the price and quality seems all over the place so looking for suggestions of one that works without spending too much.

 

[Mr Chibs]

I haven't used it (yet) but Oxalic acid is meant to be a good stain remover.

It comes in powdered form, you can mix a paste and off you go... you may need to do a bit of reading beforehand, but thought I'd offer it up as a suggestion.
I've bought some to get staining out of an old beam and some old brickwork, not had chance to use it yet though.

 

[Mike13]

It is toxic, so be careful with it. but I will consider it.
Very good for getting the black ink stains out of timber where the tannin + rust = ink.

 

[Mike13]

The main point is that I bought as HCl based cleaner a while ago, and it was weak rubbish that did not do much cleaning for the whole bottle. I am looking for recommendations about brands that actually work as expected.