After my first winter as a ponder..... I used to do periodic water changes during the winter..... Not that it really needed it, just thought the Koi would enjoy some fresh water....... Well here in West Tennessee we don't have to worry about water changes Mother Nature is taking care of it for me...... 17" of rain since January 1st, and it has rained heavily all day, so I figure about 18" now....... Keeps me busy pumping the excess water off...... But the Koi are happy and healthy so it's OK