I have VERY little evaporation from my 12gal nanocube. In fact, i hardly ever top-off. I do bi-weekly water changes and only lose maybe 1/4in of water in that time. With a few mods to the 6gal, I think you will be just fine. Trash all of the media it comes with and fill up the filtration compartments with LR
rubble. More biological filtration means less water changes. If you get it, let me know what you think. I have tossing around the idea in my head for one in my office as well.