Hi Dave,
look for horse stall stuff.. there is a product called Stable Boy which is in powder form.. it apparently neutralizes ammonia.. I've been doing some tests at home with it.. even though it helps, I don't find it made a huge difference... I find that the powder is too fine and may eventually cause respiratory problems to the mice/rats that I'm using it on.. I just sprinkle the stuff on the bottom and a bit on the wood chips too... In the US, they have a product called Woody Pet (
http://www.woodypet.com/pets.html)... this would be perfect but I don't know if I can get that stuff here in Canada or not...
Anyways, let me know what you find out about this, as I'm very interested in this (probably as are tons of people hehe)...
Good luck,
Bristen.