I am going to make a little change to my pond, so I am going to lower the water level about 15"...... It's a 3000 gallon pond so I think I will take anywhere from 700 to 900 gallons out..... It's a one day project and the filtration will still be running just shutting off the skimmer and still using the bottom drain and 50% of my pond is 42" deep..... All that being said I use city water and I bought this filter to use to refill the pond.... I checked with our local water utility and they only use only chlorine... Lime.... And calgon..... No clormides..... So opinions please..... Bought off Amazon, ratings were high..... But I doubt those folks were refilling a Koi pond.... Thanks Jimmy