Homebrew PCBs

It was very inexpensive as I purchased it from a hydroponics shop 
that was closing. It was $5 for 5 gallons of 89% concentration. I 
did not notice the evaporation issue and while etching I did not 
notice any smell. Does anyone know what chemical reaction is going 
on?? I think it is making copper phosphate. I will try another test 
and let everyone know how it went.