Homebrew PCBs

OK, I made up some of this stuff...2/3 peroxide and 1/3 acid, and it 
worked fine the first time. Nice light green color when done, so I set 
it aside in a sealed container for next time. 2 days later, I went to 
etch again, and the stuff is dead. Peroxide doesn't reactivate it, and 
the color is still light green. What am I missing?

thanks, Jim