I have never used anything. I have read that many people use tank water but in return they usually have a lot of issues with there saw.
I use my saw nearly everyday and not an issue at all, only the switch went out and of course that has nothing to do with it.
As stated above, the coral are wet enough. From what I have found adding saltware or lots of water will only ruin the bearings. This is what Inland told me as well.