[zeestephen]

The main reason you put chlorine in a non-public pool is to prevent a ring of algae from growing along the entire water line perimeter.

[fireman15]

The main reason you put chlorine in a non-public pool is to prevent a ring of algae from growing along the entire water line perimeter.

There is that. But basically, if you do not use chlorinating chemicals or a “salt water” system... your water turns cloudy, green and slimy after a fairly short period of time, and it looks disgusting.

[woodbutcher1963]

Yes, and it can literally happen in less than 24 hours. Unless, you completely cover it so that know sunlight can get in. Algae will still grow, just not as fast.

That is no of the reasons to cover a swimming pool when not in use. The more light, and higher temperature, the faster algae will grow.

I had an in ground pool for 17 years. I also had a hot tub for about ten years.
IF I ever put in another pool, I would build it in a rectangular shape with a motorized retractable cover built in. Keep it closed whenever you are not swimming in it. Your filter does not need to run as much. You do not need as much chlorine or salt to kill algae/bacteria.

[gundog]

Perimeter,? A good algal bloom will fill the pool. Ask my turtle.