Return from vacation to some yellow/green dusty algae on shady wall of pool

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Diannapool22

Diannapool22

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Aug 14, 2018
75
Scottsdale, AZ
Hi all,

A few weeks ago I successfully exchanged ~70% of my water to lower my CYA from >100 down to ~50. I also had a reoccurring yellow/dusty algae accumulation on one wall when the FC dropped below target. (Was costing me a fortune to maintain such high FC, and I'm sure had lapses +tons of sun exposure in AZ summer allowing algae growth). After the exchange, I SLAMmed the pool and it's been a breeze with no issues. Water has been great, it's so much easier to maintain a properly chlorinated pool at this CYA level! I've been adding liquid chlorine each night to keep FC in the 4-8ppm range. However I went out of town for 4th of July, threw some tablets in the pool prior to leaving, and came back 4 days later to find some yellow dusty looking algae on the shady wall where it was accumulating prior to SLAM. I tested the FC as soon as I got home and it was only 2.0ppm, (below 4-8ppm target). It's very minor, and brushed off easily. It's been a few days now and with maintaining water in proper FC range, there's been no sight of the algae substance. Do I need to SLAM again due to the reappearance of the dusty substance when I know FC was too low? Or can I simply maintain the water in the right range and not worry about it? Water is crystal clear. Thank you!
 
Okay, did OCLT. 7/9 10pm FC= 6.5ppm, 7/10 6am FC= 7.0ppm. CC= 0.5 both times. FC shouldn't be higher, but I'll chalk it up as testing error. I gave the pool a good brushing yesterday afternoon as I was starting to see a bit more yellow accumulating on the same wall. Unsure if it was leftover from the weekend and I didn't see it the first time, or if it was slowly coming back. After looking the through Mustard Algae post and threads of those who have it... I am afraid to admit I think that's what I have. Would mustard algae show up on OCLT?
 
Go straight to MA. That is 60% of your CYA level for 24 hours only. Then keep your FC at 15-20% of your CYA level for several days to a week to see if the MA comes back.
 
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Okay will do. 60% of CYA= 50 means 30ppm FC for 24 hours, then 20% of CYA is 10ppm FC for a few days. Seems very doable. Will lower pH prior to starting as well as doing all other SLAM procedures. I wish I would have finished the previous slam with MA SLAM for 24 hours. Figured there was no way I had mustard algae but given that it's still present and matches the appearance/description posted on this site, it's got to be that.
 
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If my CYA gets to 50 ppm in the summer, my FC loss goes really high. AT 70 ppm, it stays around 4-4.5 ppm FC per day.

I can tell when the CYA drops to 60ppm, as the FC loss starts to increase.

Be sure to test your CYA monthly. You will lose about 15-20% of your CYA each month from May to September.
 
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Each 8oz puck would raise the CYA in your pool volume by 2 ppm. Use Poolmath.

As you are using liquid chlorine, dissolving two or three pucks in a floater would not be a bad idea. Will add the CYA and some acid.
Be sure to continue to test FC and add the required liquid chlorine every day. You would need to do that 3 times or so to get the CYA increase you want.

Or, for more instant gratification, get CYA aka stabilizer / conditioner and put the required amount for 10-15 ppm CYA in a sock and dissolve it by hanging it in front of a return.
 
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