I used to use Windex on the freshwater tanks without any problems, but once the first saltwater tank was up and running I stopped using it on any of them, which turned into a big deal since we had 7 tanks in the house at the time. Another person from MR told me I didn't need to worry about those kind of chemicals since I had a nano with a top on it but I didn't want to take any chances. Unfortunately I'm one of those people who can't get away with anything so if Windex was going to be a problem with anyone's tank it would be mine. The microfibre cloths work really well, although I'm a fan of that polishing small spots with my fingertips, and now that I've only got the two tanks it doesn't take all that much time.