How much water does your tank evaporate each week and how large is your tank? Do you take any precautionary measures to limit the evaporation amount?
I go through about 30 gallons a week on a 240 gallon tank. Feel like that is a lot, but in my past set up, I didn’t monitor it as closely as I do now. My Rodi used to run to my ato non stop refilling it. After I moved, I had space for a small fish room so I switched from a 5 gallon bucket to to 32 gallon brute can. I let it run out before I refill. Which is also WAY better for your RoDi cartridges!
There are many variables which effect evaporation. One is the amount of humidity in the room.
Evaporation tends to be higher in the winter months as heating systems dry out the air as the house is warmed. During the summer, higher humidity translates to slower evaporation.
Invest in an auto top off system to address this issue.