When I tested RO at work using TDS meter I got around 16 ppm, Purified water around 20 but Distilled water by the gallon, sealed ones at grocery stores I got 0ppm. I am using Distilled water and no problems with brown algae. Hope this helps.
Been using Distilled water the sealed ones not the dispenser type from grocery stores, Target or Walmart and no issues and 0 on my TDS meter. Maybe somebody can chime in with their readings with RO water.
If ro water is reading higher than 0.. Its due to poor maintenence in the unit. A lot of "distilled" is in fact ro water it will actually say distilled by ro sometimes.. Standard distilled water does not compare to the quality of ro on a tds.. Standard evaporation and drip distilling wich removes chlorides and other solids does not Leave you with a 0 tds more like a 60 to 100. Ide say the water source of choice uses an ro unit.. Be careful though a lot of water that way adds back in sodium chloride and calcium chloride for flavor purposes too.
