Please who knows what chemical to use or how best to wash off green algae from interlocking stones and walls.

No response?

Have not tried it, but read you can use very very mild acid solution (Hydrosulphric, same as battery) acid for bricks and roof tiles.

Not sure how it goes with calcium Carbonate in your concrete tiles, but you can experiment.

If its reacting, I think a mild solution of caustic soda (NaOH) might do it better being a base and toxic organisims

Ok did a little google check-

Sulphric acid will react a bit, expose new surface and make you stones look new. You need to rinse well with water after, not good if you have pets. Wash off Might be good into smelly drains.

You can also use bleach - hydro chloric acid. Mind your work cloth for colour bleches.

Caustic Soda will not react with CaCO3 in concrete. Will not etch the stones but Moss will die, turn black from green

Something else popped up, Sodium Crystals. Not sure which Sodium salt people use, but its not NaCl.

Cheapest method and Environment friendly- Boiling Hot Water and wire brush

Get chlorine, soak it and use it to wash it.

Thanks guys for your contributions.

Hello.
Please did any of the above help? I need to clean my interlock brick as well.
Thank you for your anticipated response.