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

Diannapool22

Well-known member
Aug 14, 2018
69
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!
 

Diannapool22

Well-known member
Aug 14, 2018
69
Scottsdale, AZ
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?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,229
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
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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Diannapool22

Well-known member
Aug 14, 2018
69
Scottsdale, AZ
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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Diannapool22

Well-known member
Aug 14, 2018
69
Scottsdale, AZ
@mknauss I see you have a SWG, but with a similar climate in NV I'm wondering if you know what a "normal" loss of FC during a hot sunny day is with CYA at 50? I'm sure there are a lot of factors, but I'm thinking somewhere in the 2-3ppm range.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,229
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
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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Diannapool22

Well-known member
Aug 14, 2018
69
Scottsdale, AZ
Just tested CYA. It's 40. What is the math/method to raise it using pucks? 1puck= xx CYA increase?

Or do you recommend a different stabilizer? I think I would do better between 50-60 range. Thanks
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
37,229
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
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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