Re: Baking soda...safe?
I use vinegar and water to clean my cages during my weekly cleanings. However, I, too noticed that it doesn't always seem to help with the stains from urine on the coroplast. Since then I've continued to do weekly cleanings with the vinegar and water and then once a month I do a more thorough cleaning that includes using baking soda. After doing this for years, I have noticed no ill effects.
Before I began using the baking soda, I asked the advice of my cavy savvy vet. They said that they've never heard of an instance that proved baking soda to be dangerous, but cautioned me to rinse well and let it sit out for a while before returning my pigs to their cage. This has worked well and my guinea pigs certainly don't mind having the extra floor time.
It hasn't worked miracles, but I do see a difference after cleaning. After about a year, though, I do purchase new coroplast. But it has helped maintain the coroplast longer in the meantime - at least in my opinion.