I have a pool that has been extremely difficult all season. Initially one of the other guys at my company was working on this pool. It was green when we started. After a month, it was still green. At that point it was given to me to figure out. I shocked the pool hard (12lb of trichlor) and kept as much chlorine flowing into the pool as I could. I completely filled the automatic chlorinator, and I put two floaters in the pool. I was using about 20 tablets/week. The pool went from green to a nice cloudy blue overnight, and within two weeks had cleared up.
Now that the pool had cleared up, I cut back on the chlorine in a big way. I took out the two floaters, and I cut back the chlorinator too. I left it running a bit high thinking that I can always turn down the chlorinator more next week, rather than turn it down too much now and have it turn green again. This was all happening during the hottest week we've had all summer (high 90s). So I had to guess how much would be enough. I was pretty close. The pool made it 6 days. When I got there on day 7 it had clouded up again. I spoke to the owner, and she said she was in it the night before and it was crystal clear. When I tested the water, there was still a reasonable amount of chlorine in the pool (probably around 5ppm). So I've been fighting with it ever since.
I raised the chlorine way up using the chlorinator and the floaters. After about a week, it was almost clear. I could see the Main Drains in the bottom. After a second week, it is cloudy again. Yesterday, when I was there, I tested the water and the FC was over 20. The filter was replaced earlier this season, and is producing a good cloudy backwash every week. The pool was treated for phosphates about two weeks ago (I know how you all feel about phosphate treatments, but it rules out phosphates as a contributing factor).
As of yesterday:
Fiberglass Pool, Sand Filter, using 7day Tablets. Running 24/7, and serviced at least once a week.
Does anyone have any idea what is going on here? Apparently this pool has been difficult for years, and that is why they fired the last guy who took care of the pool and came to the company I work for. He never figured it out, and he didn't seem to come up with anything to even try (like replacing the filter). What could be making this pool so difficult?