I live in a very small apartment and all of my rats are housed in my living room, so I have been extremely paranoid about my house smelling like must/pee. But of course, rats don't do well around perfumes and aerosol, so keeping the smell covered up with fresheners was a no-go. I can't afford to dish out over $150 for an air purifier.
I tried just keeping boxes of baking soda around their cage to absorb the smells in the air, but that simply didn't cut it. However, I found that putting a light layer of baking soda on the bottom of the rat tub under the bedding works wonders! A medium sized box of baking soda lasts me about a month with 4 3'x2' cement mixing tubs, and seeing as it only costs about $1.50-$1.75 per box, it seems reasonably affordable.
Of course, this method may still not work for someone with overcrowded rat cages, or kept in under-ventilated places.

Anyone else tried baking soda to help with the smell in their tubs? Any concerns associated with rats and baking soda?