Where is Waterkeeper?
No it will not eliminate all algae, not even close. All the food you put into the tank stays there and becomes plant food. Food contains nitrogen and sometimes phosphates. The animals themselves add ammonia and CO2. These things equal algae. But if you are using tap water this just adds to the nitrates and phosphates already there and it is cumulative. My tap water here in NY has a nitrate reading of 10. If I continousely add this, it will just keep rising. At least RO water eliminates these pollutants.
I got my bare bones RO/DI on line. I just connected it to a 5 gallon bucket and built a float switch that turns off the electric valve that feeds it. All RO units work basically the same so it doesen't really matter which one you get, the important thing is the membrane that is in it. Some of them only reduce the pollutants 90% or so which may let through enough chemicals to harm your corals which happened to me twice. You also need to decide how much water you need to make daily. Some of them only make 5 gallons which may be fine while others can make as much as you want. My unit makes 15 gallons a day but my tank only uses one gallon a day. I like the 15 gallon size it just takes me a couple of days to make enough for a water change.
I am charging Waterkeeper per word. This is his job.