Hello Guilletto! From your description I'm guessing you have this model in medium or large: Exo Terra : Waterfall / Natural Waterfall. Water will evaporate so you will have to replace it. Adding the optional fogger will require closer monitoring because your water level will go down faster. Not sure what is your unit relationship between the Repti Flow 200 pump and the optional Fogger. According to manual they work as separate systems: http://www.exo-terra.com/download/pr...ion_Manual.pdf. Could it be that with fogger installed the output tube is smaller and that makes it look as a higher flow? Good luck !