Partly Cloudy, No CC's

[OneMom]

Hi All:

I'm so glad I found this site earlier this summer. Our pool has really been pretty "Trouble Free" since.

However, in the last 4-5 days it is somewhat cloudy. We have accumulations along the bottom around the seams of powdery green/yellow stuff. When we brush each day the stuff lifts off the bottom in a cloudy bunch & disaappears. Just agitating the water dissolves it - no strong scrubbing is needed. I've been reading the comments here about pollen...I think that might be it, but I'm not sure. It has been in the 90's and humid for the last 5 days here in the Milwaukee, WI area.

We had stopped using our auto chlorinator this summer due to CYA levels, but we have had it on in the last four weeks due to convenience/busy schedules. We test the water every day w/Taylor's FAS/DPD kit. Here's today's readings:

CYA: 70
FC: 6
CC: 0
PH: 7.3
TA: 95

Since it's been days of the water being slightly cloudy wouldn't we be seeing some increase in our CC's if this is the beginning of an algae bloom? Is it possible to have algae in your pool & not show any CC's?

Thanks!

 

[divnkd101]

How long has it been since you have backwashed????

 

[JasonLion]

With plenty of sunlight and chlorine you won't always see any CC, even when fighting algae. If your chlorine demand hasn't gone up significnatly recently I would suspect dirt/pollen.

 

[duraleigh]

Do you have pollen in Milwaukee in July/August?

 

[OneMom]

We backwash every other day (approx.) - it just depends on the pressure guage. We do have pollen here in WI at this time of year.

However, this afternoon our water is starting to look green. I'm going to shock it to 20. Since my CC's are 0, how long should I keep it at 20?

We're pretty baffled. I don't understand how we can prevent algae in the future if we can't rely on seeing an increase in CC's.

 

[Poseidon]

We backwash every other day (approx.) - it just depends on the pressure guage. We do have pollen here in WI at this time of year.

However, this afternoon our water is starting to look green. I'm going to shock it to 20. Since my CC's are 0, how long should I keep it at 20?

We're pretty baffled. I don't understand how we can prevent algae in the future if we can't rely on seeing an increase in CC's.

Combined chlorine cannot be used to predict when algae will bloom. Even with a minimal algae bloom, CC will not always be present. A heavy algae bloom however will usually produce CC. You can prevent algae by maintaining a free chlorine level of 11.5% of the cya level .... in your case that would be 8.1 ppm FC. You will probaly need to go quite a bit higher than 20 ppm to kill the green algae quickly (if it is algae) ... closer to 28 ppm FC (which may be pushing the upper limits of vinyl, I don't know what type of pool you have). You will need to maintain 28 ppm until the pool does not use any chlorine overnight, and CC is less than .5 ppm.

 

[OneMom]

"You can prevent algae by maintaining a free chlorine level of 11.5% of the cya level .... in your case that would be 8.1 ppm FC. You will probaly need to go quite a bit higher than 20 ppm to kill the green algae quickly (if it is algae) ... closer to 28 ppm FC "

Wow...that must be the problem. We've been using the "Best Guess" chart, and keeping FC within the indicated range on that chart. We haven't had our FC drop below the recommended range in almost a month.

Actually, the lowest FC level we've had in weeks is the current level of 6ppm. We keep a daily log of our test results and we haven't had an FC reading lower than 9 in weeks. (Plus our CYA level was lower...it's only gone up in the last couple weeks due to us using the auto chlorinator.) I guess this current drop of 3ppm signaled the onset of the algae. I didn't realize that a drop that small could be significant over 7-10 days. We assumed the drop was due to the heat wave & our solar cover being off in the last week.

I'll have to stop using the "Best Guess" chart & start figuring 11.5% of the CYA level. Is this the method everyone has been using lately?

 

[duraleigh]

I'll have to stop using the "Best Guess" chart & start figuring 11.5% of the CYA level. Is this the method everyone has been using lately?

No.

Use Chemgeek's best guest chart located in the stickies above. I don't want to speak for Richard but I believe he has taken Ben's best guess and, through his own data he has gathered and his knowledge of chemistry, has (modified, tweaked, refined) the chart to more accurately reflect real world condition. (Richard, I apologize if I butchered that explanation)

Anyway, while Poseidon's data does not look unreasonable, I'm not sure how it was calculated so, until more info is available, I would suggest Richard's chart as the defacto reference for CYA/chlorine relationships.

 

[JasonLion]

Ben's Best Guess chart has worked correctly for many many people. I only known of two exceptions to his chart. People with reocurring mustard algae have sometimes needed to keep their FC level at or above Ben's max column and shock well above his shock column. And at CYA levels over 150 his numbers might be a little low, but you don't want to be there anyway.

Recently there have been a couple of different people working on revisions to Ben's chart. My Pool Calculator, see the link in my signature, makes FC level suggestions that are very similar to Ben's but differ in some minor detals. Chem Geek has also developed a chart, which is where I believe the 11.5% that Poseidon mentioned came from. The 11.5% rule is designed to track about half way between Ben's min and max column and is known to have problems at very low CYA levels. The nice thing about the 11.5% rule is that it is fairly easy to remember (if your mind handles numbers at all well).

Different pools need different FC levels. That is why Ben made min and max columns. The 11.5% rule simplifies that into a single number, which is nice, but it hides the variation that exists between different pools.

Anyway, lets get back to your problem. I would adjust your PH to between 7.2 and 7.4 and then shock to 20. Keep it up there until it holds steady overnight and CC is zero and then hold it there for another 24 hours. That will take care of any green algae and all but the very worst of the reocurring mustard algae. Since you don't have a history of mustard algae problems I don't expect that will be an issue. While that is happening brush the entire pool every day.

 

[duraleigh]

Jason,

I apologize for not giving you credit for the work you've done. My assumption was that you had taken Ben's numbers and used them for the basis of your calculator. I would certainly use the numbers you have developed and was wrong not to have given you full credit for it.

Poseidon, I certainly meant no offense to you, either. I was unfamiliar with numbers that specific and had no idea of their source.

 

[Poseidon]

Jason,

I apologize for not giving you credit for the work you've done. My assumption was that you had taken Ben's numbers and used them for the basis of your calculator. I would certainly use the numbers you have developed and was wrong not to have given you full credit for it.

Poseidon, I certainly meant no offense to you, either. I was unfamiliar with numbers that specific and had no idea of their source.

No offense taken, my friend. Richard goes into some detail about his chart in this thread.

 

[OneMom]

Thanks to all of you for taking the time to answer my post. I definitely have learned some valuable information!!