I run a tunze nano in a sumpless 25 gallon cube, so far I haven't had any issues with salinity swings from the evaporation. I had this same problem and really thought hard about the xp sumpless ato. Ultimately, I decided against it as I didnt want more things in the tank.
One more thing you might want to take into account is surface skimming. I didnt have a viable way to skim the surface, so I had to add in a small aquatop surface skimmer. While it's smaller than the sumpless ato, its still another thing in the tank to consider.
One more thing you might want to take into account is surface skimming. I didnt have a viable way to skim the surface, so I had to add in a small aquatop surface skimmer. While it's smaller than the sumpless ato, its still another thing in the tank to consider.