Algae bloom and not sure why.

One thing that would help I think is keeping a log of test results (or if you have them, post them) without all the extra info. It’s really hard to follow in the format it’s in and is missing lots of info.

My best interpretation is that you had a green pool, and started a SLAM on 5/25 and ended on 5/27? It’s very unlikely that a green pool with active algae outbreak can pass all three SLAM criteria in 48 hours. Maybe it’s possible, but we don’t know water test results during that time to understand what the FC level was after you added and don’t have the OCLT results to confirm what the level was one day to the next, etc.

Take it for what it’s worth, but I’d bet if you kept a log with just test results and chemical additions (and nothing else) the reason for the algae would become obvious, or would at least show you some missing detail in the process.
 
One thing that would help I think is keeping a log of test results (or if you have them, post them) without all the extra info. It’s really hard to follow in the format it’s in and is missing lots of info.

My best interpretation is that you had a green pool, and started a SLAM on 5/25 and ended on 5/27? It’s very unlikely that a green pool with active algae outbreak can pass all three SLAM criteria in 48 hours. Maybe it’s possible, but we don’t know water test results during that time to understand what the FC level was after you added and don’t have the OCLT results to confirm what the level was one day to the next, etc.

Take it for what it’s worth, but I’d bet if you kept a log with just test results and chemical additions (and nothing else) the reason for the algae would become obvious, or would at least show you some missing detail in the process.
Sorry, the format sure has some room for improvement. The SLAM is generally a 10-14 day process, as in this case. The FC was raised ~10 days prior to 5/25. With my work schedule, it's rare that I return home to a clear pool like I did on 5/25. For this instance the pool was not in SLAM, as the FC was down to 10.5. That night I shutoff the SWG so I could get an idea of overnight FC loss after vacuuming the pool. I then went into troubleshooting the SWG output and even second guess passing the SLAM criteria on 5/30, because the oversized SWG running 24/7 and not keeping up.

Looking back on it all, I'm convinced all three SLAM criteria were passed twice and pool left balanced at a FC 3 times the apps recommended minimum and 1 ppm below the maximum. Upon discovery of green pool, it was still 2 times higher than the apps recommended minimum. When I return home next week, I will be pulling the ladder and lights to inspect. Currently the pool is cloudy, but the filter pressure hasn't increased yet. I'll have family add some DE today to assist.
 
Besides inside the ladder rails, here is one today from the bottom of the ladder steps. With a repeat SLAM, you missed *something* the first time and every inch needs to be scrubbed and inspected.


 
Alright, I made it home this afternoon and obtained the readings below. I don’t see a way to add phosphates, but they are 500 ppb. The water was clear before the kids brushed it, now it’s slightly cloudy. There was a little bit of drop out in liner seams. What should I do next? Usually if it’s clear with some dropout, I would vacuum the drop out, then brush. If it was still clear after brushing, I would complete overnight test. I am losing about 3 ppm per day with SWG running 24 hours. Heat index has been around 100.
==========================================
Home
------------------------------------------
Build Type: Vinyl
Volume: 27000 gallons
------------------------------------------
Latest Test Result Summary:
FC: 8.5 (40 minutes ago)
CC: 0.5 (40 minutes ago)
pH: 7.2 (40 minutes ago)
TA: 70 (40 minutes ago)
CH: 125 (40 minutes ago)
CYA: 50 (40 minutes ago)
SALT: 3600 (40 minutes ago)
BORATES: 15 (40 minutes ago)
TEMPERATURE: 91° (40 minutes ago)
CSI: -0.98 (40 minutes ago)
==========================================
 
Full SLAM ahead. Your CYA should be 70 and maybe even 80 for the LA heat. That could be part of the problem where you hit minimum while away but with some cloudy days it was back in target (with a bloom) when you returned. For now, SLAM at 50 for the lower FC target.

Get the ladder out and cleaned. It's clearly growing on the surface of the pool so every inch needs inspecting / cleaning again.
 
Alright, I made it home this afternoon and obtained the readings below. I don’t see a way to add phosphates, but they are 500 ppb. The water was clear before the kids brushed it, now it’s slightly cloudy. There was a little bit of drop out in liner seams. What should I do next? Usually if it’s clear with some dropout, I would vacuum the drop out, then brush. If it was still clear after brushing, I would complete overnight test. I am losing about 3 ppm per day with SWG running 24 hours. Heat index has been around 100.
==========================================
Home
------------------------------------------
Build Type: Vinyl
Volume: 27000 gallons
------------------------------------------
Latest Test Result Summary:
FC: 8.5 (40 minutes ago)
CC: 0.5 (40 minutes ago)
pH: 7.2 (40 minutes ago)
TA: 70 (40 minutes ago)
CH: 125 (40 minutes ago)
CYA: 50 (40 minutes ago)
SALT: 3600 (40 minutes ago)
BORATES: 15 (40 minutes ago)
TEMPERATURE: 91° (40 minutes ago)
CSI: -0.98 (40 minutes ago)
==========================================
That is hot water!
 

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FC back to SLAM level. Pulled ladder and cleaned. Had a little green bloom come out of ladder when I knocked off the rubber cap. I didn’t remove the lights, I’m not certain how it comes apart without messing it up.
 

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Those lights are nicheless and water can't get behind them. The ones to worry about is where the light sets into a larger niche that gets water behind it to help cool the light. I would just scrub around those really well with an old toothbrush, especially where they meet the liner.
 
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