I've been a pool owner for 10 years in New England, but recently moved to SC, where I have a small pool with spa (4,700 gals).
Because of the low pool volume, it has been tricky keeping my Cl level where I want it. I have an inline chlorinator that I have to keep almost closed to keep the Cl level down to normal levels.
In the process of trying to find the right setting on the chlorinator, I let the Cl level drop to 1ppm. And then I got some algae spots. Nothing big, just annoying. I shocked to pool to 15-17ppm (for three days), brushed and vacuumed. Everything was fine until I let the Cl level drop to 7.5-8ppm, then the algae starting showing up again. I hate to think I'd have to have a higher shock level and keep it there longer, but that's what I'm leaning toward now.