Karen,

You will not harm ipe by not staining it. You may get a bit more checking of the wood, but it won't be significant. The Atlantic City boardwalk and many park benches in NYC are unstained ipe and they have been holding up in some cases for decades.

If you want to get rid of the grey color then a percarbonate cleaner sold by Woodrich, EFC-38 would work well as it has some additional ingredients in it that act as a mild stripper. It is the exact same product as RAD, which is no longer for sale as far as I know. You would have to apply it, let it dwell 20 minutes, and brush it with a deck brush, and then rinse. Depending on how it looks you may not need to use the brightener, whose primary purpose is to neutralize the high ph of the percarbonate cleaner prior to staining. If you want to maintain the grey color of unstained ipe they you mostly want to get rid of any mold, mildew, and dirt. For this you could either use a straight percarbonate cleaner, which you can buy directly for very little from the Chemistry Store (chemistrystore.com) or use a mild bleach and water solution ( 1 part bleach 8 parts water) with a bit of dish detergent mixed in. Same method as percarbonate cleaner, let it dwell, brush it lightly, and rinse.

By the way, the first time a stain is used on Ipe it typically only lasts a few months. After that you can usually get close to a year before you need re-staining. I use Cabot's ATO and now after re-staining yearly for 3 years have enough residual stain left on the deck that I don't need to re-stain it this year. The color has faded only a little and looks quite uniform in tone. The stain is duller in appearance though from when it was stained last May but looks presentable. All I did this season was to mop on the mild bleach/soap treatment.

Hope this helps,
Marty