Algae every 2 wks despite maintaining FC of 7+ in SWG pool

[dsharp]

It came back today. Here are my readings

FC - 8.0
CYA - 60 (though I usually keep it closer to 75)
TA - 70
Salt - 3100
pH - 7.5

I don't understand why it keeps coming back. I run the pump on high 12 hours a day. The FC stays high. I haven't been running the SWG much because the FC has stayed double digits since the last shock.

It is unusual the CYA dropped below 70 (probably because I added water to the pool 2 days ago with the FC at 11) and it has been very sunny since, but should that matter when the FC stays so high?

 

[jparr]

I have been having the same issue. Mustard Algae coming back after lots of scrubbing and shocking. I just got done with a four day Mustard Algae shock, no signs of any. I'm waiting to see what if anything grows. Like you, I was keeping my FC levels around 10 with a CYA of 60ish, and seemingly having no affect on the algae growth.

 

[Guest]

Have you shocked your pool at 18ppm and did an overnight chlorine test for loss? Have you cleaned your cartridge filter? what is your pool water temp?

 

[bk406]

Like you, I was keeping my FC levels around 10 with a CYA of 60ish, and seemingly having no affect on the algae growth.

Mustard algea is tough to get rid of but enough chlorine will do the trick. At 60 ppm CYA, shock level for mustard is around 35 ppm. If it is mustard, you dont have near enough chlorine at 10 ppm to even touch it.

 

[dsharp]

Have you shocked your pool at 18ppm and did an overnight chlorine test for loss? Have you cleaned your cartridge filter? what is your pool water temp?

I shock it to at least 22-24 ppm, sometimes higher. I leave the SWG going to maintain FC levels while it's clearing. I clean the filter every 2-3 weeks (not since last algae about 2 weeks ago, though). Pool Temp has been around 85.

 

[Guest]

bk406, hit it right on, if it is mustard algae, with what data you gave us, you need to shock around 35 - 38 ppm.

 

[chem geek]

Yellow/mustard algae is about twice as slow to kill as green algae so shock levels need to be higher. It also likes shade so can hang out behind light niches and under removable ladders. You need to put in poles and other equipment that would get back into the pool at some point after shocking. Also, keep the high shock level for at least an extra day beyond no visible algae, <= 1 ppm FC overnight drop and <= 0.5 ppm CC. If any of the algae survives, it can grow again unless the FC is kept at around 15% of the CYA level which can become impractical/expensive which is why it's better to completely kill it if possible.

 

[dsharp]

bk406, hit it right on, if it is mustard algae, with what data you gave us, you need to shock around 35 - 38 ppm.

Are you answering me or jParr? Are you saying mine is likely mustard algae, too? The regular 24 ppm shock does seem to take care of it for the time anyway. Mine's not under shade or removable ladder necessarily. However, it does appear to begin in areas where the water doesn't circulate as well i.e. furthest from the return jets.

 

[benavidescj]

dsharp, what does your algae look like? I do not see a CC or TC test result in your post. Have you done the overnight FC test? If not I recommend you do so and post those numbers so we can help you out. Without those numbers it is hard for us to determine if you have algae. It may look gone but the test may prove otherwise.

 

[Bama Rambler]

How are you testing?

One thing bothered me in your initial post.

I haven't been running the SWG much because the FC has stayed double digits since the last shock.

When and what was your last shock?
And, what's "not much" run time for the SWCG?

 

[dsharp]

How are you testing?

One thing bothered me in your initial post.

I haven't been running the SWG much because the FC has stayed double digits since the last shock.

When and what was your last shock?
And, what's "not much" run time for the SWCG?

I shocked about 2 weeks ago (last algae sighting) Since then the FC stayed so high I had the SWG off or, for the last couple of days, at 25% during the 12-hour pump run I give it each day. Normally, I run it around 40% to maintain. CC was 0 - 0.5. Overnight I lost 0-0.5 FC so I'm sure the algae was gone. If it comes back, I'll make better note of whether it was more yellow-ish. I hadn't considered that.

My theory - One thing that may contribute is the two 50-lb sand bags in the pool that weigh down the steps are enclosed in giant "baggies" and there always appear to be algae INSIDE the baggies. I figured it was staying sealed in there, but it could be some gets out and feeds into the pool. Possible?

 

[benavidescj]

Repeating Dave's question, how are you testing?

 

[Bama Rambler]

You need to open those sand bags and get some chlorine in there. If algae got in algae can get out.

If it were me I'd get rid of those bags and use 5 gallon buckets instead. Fill them with sand and water then add a pint of bleach to each and close them up tight.

 

[dsharp]

Repeating Dave's question, how are you testing?

I have the TFP test kit and test for FC and pH every day; CYA about once a week. TA every two weeks or so as that doesn't seem to fluctuate much. The SWG has an automatic readout for Salt level.

 

[dschlic1]

Some types of organics love to hide. For example on my pool, they were hiding in the air piping of my spa jets!. Until I ran shock level water back through the air piping I was in the same boat.