When I cleaned my red brick wall it has become green likean algae colour, why is that?

Question

When I cleaned my red brick wall it has become green likean algae colour, why is that?

Answer 1

Did you clean it with muriatic acid?  That's the reason.  Especially if you left it on too long, OR if you didn't pre-wet (saturate) it, and rinse thoroughly afterwards.  Its "acid burn"  also known as "vanadium stain".  It may be permanent.  You could try to fix the vanadium stain with something like Sure-Kleen 800, but no guarantee.  You may have to live with it, or replace the bricks, or have them tinted by a professional tinting company like Nawkaw to match the original colour.  

Stop using acids and bleach !!!   Follow directions exactly if you use SK 800  

(not to be confused with Sure-Kleen 600 ).  

You can get it through a professional brick distributor,

NOT through Home Depot / Rona / Lowe's.

Answer 2

You must have already had a problem with this wall, which caused you to wash it now. You have told us very little about the problem and why you needed to clean it. Algae takes some considerable time to grow on a brick wall so I do not think it is that, maybe you could expand your question

Answer 3

The brick is holding moisture.  I have seen this problem on my brick house when we get a lot of rain and the weather is warm.  Get a spray bottle and use a 50/50 mix of bleach and water.  Spray down the algae and see if that helps.