Is a Light Dusting of Algae Normal while Brushing?

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CaptainUnderpants

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Aug 14, 2017
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Long Beach, CA
Just looking at the pool you wouldn't notice any algae, but when I brush some green algae is kicked up and when I clean the cartridges filters there is a light hue of green on the unwashed cartridges. Should my cartridges ever have a green hue if my pool chemistry is correct? Do I need to shock the pool? Here are my specs:

11,500 gal salt water black bottom pool, running filter about 10 hrs a day at 1200 rpm, IC40 set on about 50%, the pool remains covered quite a bit and temps are around 81 - 86 degrees. The pool chemistry is very regularly checked with a taylor 2006 and is as follows:

FC = 8.0 - has been in the range of 7.2 -9 and not dropped below the 7.2
CC = 0 - kind of strange, you think there would be some if there was any noticable algae
PH =7.5
ALK = 90
CA = 390
CYA = 70-75
Salt = 3600

Is there just not enough circulation in my pool, do I need to brush it more often than 2 times a week, do I need to shock the pool? I guess I am just a little miffed as to how there can be any algae at all with the numbers I have. Thanks in advance for your experience and wisdom.
 
Do this test please:

Pool School - Perform the Overnight FC Loss Test (OCLT)

BUT saying that I will also say you should not see any dusting of algae nor should there be any green on the filters. I will share that if I am not able to brush my pool at least 3 times a week I start to see less sparkle in my water and have even found some algae on the side of the pool wall. You will need to find what works best for you and your pool. Each pool is so different.

I would think about doing a SLAM as seen in this link:

Pool School - SLAM - Shock Level And Maintain

It should be a short one as it is for a small amount of algae. The overnight test will be interesting to see.

Kim:kim:
 
Kim, thanks for the reply. My pool passes the OCLT test, so starting a shocking process today. While algae is not present in any type of force, I think completely eradicating any presence is what is required. The only other thought is that maybe my CYA is higher than I think, as the testing mechanism allows a little room for interpretation, keeping the chlorine from doing its job. Slaming the pool should take care of it. Then keep an eye on it.
 
Oh me, oh my how I dislike the CYA test! Here is MY way of doing it to save my sanity!

CYA-GLANCING in at the dot. Do NOT stare or look for it........you will see it :roll:

-mix the solution and let it sit for about a min. (I mix it first then run the rest of the tests). Invert the mixture one more time. I don't "shake" it. I invert the bottle a few times to mix it.

-Pour to the 100 line (first line)- GLANCE in, if you see the dot pour to the next line, GLANCE in, keep going until you do not see the dot at a GLANCE!

-Call it at the line you cannot see it at a GLANCE!

See how that goes. I will check in with you tomorrow.

Do you have a light in your pool? I would think about taking it out and see what, if anything, is behind it.

Kim:kim:
 
kimkats said:
Oh me, oh my how I dislike the CYA test! Here is MY way of doing it to save my sanity!

CYA-GLANCING in at the dot. Do NOT stare or look for it........you will see it :roll:

-mix the solution and let it sit for about a min. (I mix it first then run the rest of the tests). Invert the mixture one more time. I don't "shake" it. I invert the bottle a few times to mix it.

-Pour to the 100 line (first line)- GLANCE in, if you see the dot pour to the next line, GLANCE in, keep going until you do not see the dot at a GLANCE!

-Call it at the line you cannot see it at a GLANCE!

See how that goes. I will check in with you tomorrow.

Do you have a light in your pool? I would think about taking it out and see what, if anything, is behind it.

Kim:kim:
Click to expand...

I have been struggling with the CYA test. I even bought another bottle of the reagent, thinking the first was bad. Black dot never completely disappears. I will try your method.
 
Are you testing CYA outdoors on a bright sunny day, with your back to the sun, viewing the vial at waist height?

And, regardless of CC or OCLT, visible algae requires a SLAM to eliminate it. There is no better indication of algae than seeing it. Lack of CC alone is not an indicator of a sanitized pool, & I’ve seen mustard algae pools pass the OCLT in early stages.
 
Thanks for the replies. Kicking up the Chlorine to slam levels did solve the problem. Crystal clear now. I did double check the CYA using the 50% method and came up with 40 or 80 ppm. Maybe its a little higher than 80, but probably not far off. I will try the above method for testing CYA. I think I will let the CYA just float down over time, keep an eye on the chlorine level, and hopefully see what triggers this.

There is a pool light and a spa light, but newer LED. The pool is only about 15 months old.
 
CaptainUnderpants said:
Thanks for the replies. Kicking up the Chlorine to slam levels did solve the problem. Crystal clear now. I did double check the CYA using the 50% method and came up with 40 or 80 ppm. Maybe its a little higher than 80, but probably not far off. I will try the above method for testing CYA. I think I will let the CYA just float down over time, keep an eye on the chlorine level, and hopefully see what triggers this.

There is a pool light and a spa light, but newer LED. The pool is only about 15 months old.
Click to expand...

Can the pool pass the Overnight Chlorine Loss Test?
 
Pass the OCLT - Yes pretty much. I have results from 4pm yesterday, but obviously in sunny socal there were about 2-3 more hours of sunlight. Yesterday afternoon's chlorine was 17.2. Compared with this morning's reading of 15.8 at 8:45 with no sun. If yesterday's reading were taken later in the day, I am sure the pool would have past the overnight test.

However, I did just re measure CYA using direct sunlight, back to the sun, and more of a glance and it is fair to say that my CYA might be more like 100. Would you say that a pool with a CYA of 100 and a chlorine level of 8 could develop the algae I have described?

My hunch is it is time to drain some water out of the pool and get the CYA down. Thanks for all of your advice!
 
CaptainUnderpants said:
Pass the OCLT - Yes pretty much. I have results from 4pm yesterday, but obviously in sunny socal there were about 2-3 more hours of sunlight. Last nights chlorine was 17.2. Compared with this morning's reading of 15.8 at 8:45 with no sun. If yesterday's reading were taken later in the day, I am sure the pool would have past the overnight test.

However, I did just re measure CYA using direct sunlight, back to the sun, and more of a glance and it is fair to say that my CYA might be more like 100. Would you say that a pool with a CYA of 100 and a chlorine level of 8 could develop the algae I have described?

My hunch is it is time to drain some water out of the pool and get the CYA down. Thanks for all of your advice!
Click to expand...
There is no ‘guessing’ for a proper OCLT. I agree with your logic there, but the OCLT should not be compromised. I would check again when it’s convenient to do so properly.

Your absolute lowest safe FC is 7.5% of your CYA, daily FC target range is 12-15% of CYA. If your CYA is 100ppm, that makes a FC of 7.5ppm the absolute minimum, with a daily FC target of 12-15ppm. If you have been using FC of 8ppm as a daily target, yes it is possible for algae to quickly overtake the pool.

You are correct that you should lower that CYA.

EDIT:
I just remembered that you have a SWG. FC minimum is 5% of CYA, target is about 8%. So at a CYA of 100ppm, 8ppm would be the target.

And yes, if there are areas of poor circulation, algae could get started there, that is why it is so important to regularly brush
 

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Draining water right now, will try to get rid of about 20% of the water and refill. The algae started right about the point that FC got below 8ppm (w/ 100 CYA) and in the "Poor Circulation" areas. FC readings were 5.2 to 7.4 for quite a few days.

I think I have a good handle on the problem, thanks to everyone hear. I think I was just looking too darn hard for that black dot in direct sunlight, producing a lower CYA reading than reality.
 
That is very common.............this is the "hardest" test for that very reason. Once I just said it is what it is and stopped looking for that BLACK dot things got a lot easier! I am glad it helped you!

Captain, did you know you could become a supporting member and help us keep the lights on for you and others that might need our help? Here is a link:

CLICK HERE to Become a TroubleFreePool.com Supporter!!

It is tax deductible and you get a discount on the testing stuff! :hug:

Kim:kim:
 
After draining almost 20% of the pool water, I retested CYA. It measured 70 if I looked at a glance and didn't hunt for the black dot. For comparison purposes, I broke out the my LaMotte color Q kit to get its reading. The color Q is accurate on most tests but maybe CYA is not one of them. The color Q measured CYA at 42. I can see how my CYA got too high. I was probably trying to get the Taylor kit to come more in line with the color Q. "I think I can just barely still see that black dot, better add more reagent", and hence produced a lower CYA reading. Leading to me adding more CYA.

I guess the proof is in how the pool reacts, and it is certainly acting like my CYA was too high. After the sun went down, I measured my FC to see if the pool passes the OCLT.
 
OCLT Results - Last night at 6:30 after no more sun FC 12.2, this morning at 8 am FC is 10.8. So the pool failed. But what does this mean, I didn't complete the slamming process?

Maybe there was a problem with the order of things. The pool was slammed with the high CYA, then after FC returned to more normal levels 20 percent of the pool water was drained to lower CYA. I will re slam the pool until the the OCLT is passed. So in essence I my first slam wasn't really a slam because my CYA was too high.
 
CaptainUnderpants said:
So in essence I my first slam wasn't really a slam because my CYA was too high.
Click to expand...
I'm not sure what you mean by that.......

Shock FC level for a SLAM is 40% of CYA. For a pool with a CYA of 40ppm, shock FC level is 16ppm (40 * 0.4), for a pool with a CYA of 100ppm, shock FC is 40ppm (100 * 0.4). A proper SLAM is one that maintains the proper shock level until all three criteria are met to end the SLAM.

The only effect that a high CYA has on the SLAM is that it will require a lot of chlorine to maintain shock level. At a CYA of 100ppm, you will go through a ton of bleach, and with the much higher levels of FC, your FC losses will be higher.
 
domct203 said:
I'm not sure what you mean by that.......

Shock FC level for a SLAM is 40% of CYA. For a pool with a CYA of 40ppm, shock FC level is 16ppm (40 * 0.4), for a pool with a CYA of 100ppm, shock FC is 40ppm (100 * 0.4). A proper SLAM is one that maintains the proper shock level until all three criteria are met to end the SLAM.

The only effect that a high CYA has on the SLAM is that it will require a lot of chlorine to maintain shock level. At a CYA of 100ppm, you will go through a ton of bleach, and with the much higher levels of FC, your FC losses will be higher.
Click to expand...

My CYA was much higher than I thought probably 90-100 vs about 70. So I raised FC only to about 30 instead of 40. Kind of a partial SLAM, not the complete deal.
 
CaptainUnderpants said:
My CYA was much higher than I thought probably 90-100 vs about 70. So I raised FC only to about 30 instead of 40. Kind of a partial SLAM, not the complete deal.
Click to expand...

Ok, gotcha. That was not a SLAM at all then.

Sounds like you have a good plan, get that CYA down and complete a proper SLAM. Once you do you, will be amazed at how simple (and economical) pool care can really be.
 
domct203 said:
Ok, gotcha. That was not a SLAM at all then.

Sounds like you have a good plan, get that CYA down and complete a proper SLAM. Once you do you, will be amazed at how simple (and economical) pool care can really be.
Click to expand...

Thanks..... right now I am going to keep the FC at SLAM levels until I pass the OCLT. Until then, die algae die!

The only small consideration is that I have gone to testing FC using the 10 ml sample line instead of the 25 ml sample line during slam FC levels, so the testing is a little less accurate. I guess I will continue with the OCLT test as the FC drops back down to normal levels, just to make sure the pool continues to pass.
 

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