Thats a good point because Who can afford buying RO water from a store every single water change? IF you do the math you can get a bottle of prime for cheap and treat a lot of water but RO is 1 dollar a gallon and that may not seem like much but it adds up say you do 20% water change twice a week. One persons 20% may be 10 gallons so thats 10 dollars x 2 = 20 dollars a week x 4= 80 dollars a month and trip to the store and gas. $$$ henceforth, i renounce RO as the ultimate choice due to impracticality. I'd rather use that money on conditioner, filter pads,lighting, plants etc and fish also.