Very interesting. I guess I'm used to commercial sized stuff. My lil R/O is about the same, except I don't DI mine at all. I have no appreciable hair algae. My aquifer is a little different thought too. I'm connected to the upper Carrizo-Wilcox and have a TDS of 500 incoming when it doesn't rain a lot. The only thing I really want out of the water is the copper, lead and chlorodibromomethane (and possibly odd unknown stuff). In large systems, its the softeners and other filters/resins, then DI resin towers, then the R/O is last for a 99.9% pure reagent grade (ACS Standards) water. With that diagram your statement to check the water between the R/O and Di makes total sense. Thanks.