I have a 95 gallon tank with 10 Discus. I syphon out about 12 - 15 gallons 2 to 3 times a week straight out the window. I replace with a bucket direct from the tap and take the chill of it with a little hot water in each bucket. As thats only 6 or 7 trips from the bathroom it dosnt take long. Less than 30 minutes from starting the syphoning till finished. I put a little Aqua plus in every second bucket just to be safe. Ive been doing this now for 3 months and havnt lost a Fish.