Does a protein skimmer use up more water?

[BlueAbyss]

There will be some evap through the bubbles in the skimmer... I've been told that a skimmer can humidify air quite well, the more air through the skimmer, the more evaporation (seems logical to me).

OH yeah, you're running a fluval filter? Do you have bioballs in it? The reduced water flow through it when it was sucking air likely caused some bacterial die-off, which could cause a mini-cycle (where the nitrite could come from). As far as having nitrate, I have no idea... skimmers don't remove nitrite or nitrate, they should actually remove some waste products before they break down to that point.