Muradic acid left in over night and it would be clean 

I have had buildings where new AC systems are installed at the same time, and without exceptions, the pet occupied units will clog and need acid washing sooner, and will break down sooner.I no longer allow dogs but still allow cats.What are things your tenants' pet did that cost you time and money? 

That stuff will eat your hands right off your wrists Thats basically Sulfuric acid , if you do use it watch out for eruptions .Have a towel ready to cover the drain . 

For sanded grout, I had some VERY discolored light grey grout in a bathroom and the only thing that worked was phosphoric acid (a long time ago it was in tilex and the works) but now I think you have to order Lime-B-Gone from a restaurant supply (or amazon).I would ignore very small hairline cracks.

Any previous use of the property involve chemicals, acid or poisons?

If that doesn't work use muratic acid. 5 parts water to one part acid.

I love acid stained concrete, I enjoy the look of it, and the easy maintenance.

I could have an excellent carpenter that just don't clean up well, or a good stucco plasterer but leaves wet stucco on my brick pavers for me to clean up with muriatic acid...Give you another example. 

The Caprate (NOI / purchase price) compares this property to other propertiesIMO, CASH ROI deposited to you back account is the acid test -- if you're happy, the rest is academic, but there are those who preach the IRR as the 'true measure'

I want to do a similar type of stain to my concrete floors, but I'm not about to play around acid washing myself.