Homebrew PCBs

i tried for the first time to use ammonium persulphate instead of 
ferric chloride. i built a nice etcing tank with a heater at about 
50 degree celcius and an air pump. i used about 1kg of ammonium 
persulphate with 2 litre of water (at the first place i used much 
less ammonium persulphate, but when i saw nothing is happening i put 
more).
help!!!!!!!!!!!!! i need it very urgent!
thanks a lot,
mumin.