I have set up a 10 gallon aquarium with nothing but tap water and a simple uas. I have tested the tds at 86 for day one. I will test the tds every day for 30 days or so to see if the scrubber will bring the number down. I see no reason the the algae should not purify the tap water. And as far as I can tell running a an air pump and 23watt cfl is cheaper than replacing rodi filters.?