Hiya,
Snipe, I guess I should have said most tanks. I've red some folks are lucky to have good tap water, but most of them have way to much phosphate in it causing algea problems.
Still wouldn't hurt to get an RO unit. The difference between my tank and my friends tank is amazing. I use RO, she doesn't, but uses chemicals to "fix" her water. She's still got all kinds of brown hair algea in her tank.
Meadbhb