I read that you could use Oil-Dri (the commercial stuff they use in garages) for litter. Doesn't it have additives? I was worried that the cats might absorb something from it. If not, it looks like it might be a really cheap alternative - it's 40 pounds for about $8 here. With six indoor cats, that'd be a steal compared to what I'm using now (A&H unscented). Any thoughts?