Water clouds after turning off filter for the night

Hi, Gang!

I have been having issues with cloudy water, about every 2-3 weeks. My test results as of this morning:

TA - 100
CYA - 50
pH - 7.4
FC - 11.0
CC = 0.0
CH = 300

I've had 2 algae outbreaks this season, and have used bleach and a 24/7 filter cycle to clear the water up. I have been running the filter 24 hours a day for the past week, but last night decided to turn it off at 8pm. At 8 am this morning, I turned it back on. My wife says the water is clouding up, although slightly....I see little difference.

Our latest algae bloom started a couple of weeks ago after I turned the filter off for the night, going from a cloudy blue that day to a cloudy green a couple of days later. So it seems to me that if the filter is not running 24/7, I start seeing cloudy water and eventually an algae bloom. I'm hoping that I don't see that pattern this time around, but I figure I'd see if anybody has any advice or history with similar circumstances.

I'm at a loss: I have no idea why my pool water gets cloudy when the filter isn't running for the night. I would rather not run the filter 24/7 for two reasons: cost, and it isn't solving the original issue....only hiding it.

Any thoughts?

Sounds like you're not clearing the algae bloom all the way up. When you shock to kill the algae, you should be going to 15 ppm and holding it there, until the water completely clears and you can go all night without losing any chlorine (measuring at sundown and again in the morning before the sun hits the pool, and comparing the numbers). If you let the chlorine drift back down without having completely killed the algae, even the stuff you can't see, then it only takes a very temporary dip in chlorine levels for it to start growing again.

I'll do the OCLT again tonight.

From 7/22 to 7/27, I've kept the FC above 20.0, letting it drift back down on the 28th. On the 28th, 29th and 30th, I conducted the OCLT and lost 1.5 ppm each night. I always got to the pool around 8:00AM, but the sun had been hitting the pool for an hour or so at that point. I guess I didn't kill it all.

Thanks! I'll keep going.

We occasionally see algae that is VERY resistant to chlorine, but not often enough to really know a lot about it, except that higher chlorine levels will kill it, if you sustain them for awhile.

I've dealt with that personally, 2x, on very large pools, and my priority was always kill it NOW, and get it cleaned up. In one case, I poured (2) 55 gallon drums of 15% bleach into a 160,000 gallon pool . . . and the green stuff died RIGHT THE HECK NOW. But, that was a 100+ ppm dose of chlorine in a pool with CYA < 30 ppm. (Don't do that in a vinyl pool!!) Obviously, that's not an optimized dose; 50 ppm might well have been more than enough. But I had a community pool to open, not a test pool to experiment with.

Anyhow, that's the sort of input that leaves us lacking in real specific advice, except the advice I gave myself: "Never let this happen again!"