RSM 250 Evaporation Speed

[DACJ]

For those that has RSM250 unit, does any of you encounter rapid evaporation under normal temperature? ( 77~81 ) During the summer my tank sits about 80~82, fall and winter will sit around 77~79. Regardless of what temperature it is at, I seemed to be needing a 3 litre top up EVERYDAY! I mean, there is probably somewhere around 170~200 litre of water and 3 litre really isn't much? Just seems that I never had to top up that much with my old BC29, and this is a 100% closure unit too...