Bug in web based PoolMath?

[BillB]

The amount of bleach it tells me to add for FC seems excessive.
Example- 10,000 gal pool. 6% bleach. It tells me to add 2 cups + 5 oz to bring it up 1 ppm.
That sounds like about twice the amount required.
Thanks

 

[Bama Rambler]

1 gallon (128oz) of 6% bleach will raise 10,000 gallons of water by ~6ppm FC so then to raise it by 1 ppm you divide 128 by 6 and you get 21.3 oz to raise 10,000 gallons 1 ppm FC. Looks like PoolMath is right on.

Why do you believe it's not right?

 

[BillB]

1 gallon (128oz) of 6% bleach will raise 10,000 gallons of water by ~6ppm FC so then to raise it by 1 ppm you divide 128 by 6 and you get 21.3 oz to raise 10,000 gallons 1 ppm FC. Looks like PoolMath is right on.

Why do you believe it's not right?

The other day I wanted to raise it from 0 ppm to 16 ppm. PoolMath told me to add 2 gallons and 2 quarts of 6% bleach. I did and it raised it to 21 ppm. I checked everything twice and know I measured accurately. Just one of those things I guess. I know now the numbers PoolMath is putting out should be correct.

 

[Bama Rambler]

I don't know how you got the pool volume in your sig, but keep in mind that builders routinely overstate the volume of pools. For the most part they tend to use the complete volume if the pool was filled to the very top of the wall. Which is impossible to achieve. That may not be your case, but we've seen that a lot.

It's also possible that you got some bleach that was really fresh and the concentration was a little higher than label percentage. That doesn't happen often, but we have seen it a few times.

 

[BillB]

I don't know how you got the pool volume in your sig, but keep in mind that builders routinely overstate the volume of pools. For the most part they tend to use the complete volume if the pool was filled to the very top of the wall. Which is impossible to achieve. That may not be your case, but we've seen that a lot.

It's also possible that you got some bleach that was really fresh and the concentration was a little higher than label percentage. That doesn't happen often, but we have seen it a few times.

I measured the pool, including the various depths to calculate the volume. It's within 200 gallons of being 10,000.

 

[BillB]

I measured the pool, including the various depths to calculate the volume. It's within 200 gallons of being 10,000.

You are very helpful. Let me ask an unrelated question.
I lose CYA. I know I shouldn't except for spillage. I have very little spillage. My wife and I are up in years and use the pool very seldom. I will lose 20 or 30 ppm oF CYA per year. I guess it's not a major problem. I just add it as needed but I'm wondering why.
Thanks

 

[bmoreswim]

Bill - CYA does degrade/breakdown (whatever the correct term is) very slowly over time. See the following post for a discussion from one of our experts. Your loss of 20-30 PPM per year seems to be right in line with normal expectations. No worries, just top off as needed to your correct level.

Does CYA get used up or disappear? definitive answer please

 

[BillB]

It happened again.
I wanted to raise FC from 10ppm to 16ppm.
Poolmath called for a 121 oz jug of 6% bleach. It raised it to 21ppm.
This is a hard one to figure out.
I'm using WalMart's 6% bleach.

 

[proavia]

Just to verify, you are using the web based PoolMath found here: PoolMath

You entered 10000 gallons under Size
In Now column for FC you entered 10
In Target column you entered 16
In white box to right of that you entered 6

Result should have been 125 oz. - basically almost 1 gallon.

How long after addition - with pump running - are you measuring FC again?
Are you taking the sample from about 18" deep and from the same location as the first sample?
You are using plain old 6% bleach and not the 10% Pool Essentials Walmart product?

 

[BillB]

Just to verify, you are using the web based PoolMath found here: PoolMath

You entered 10000 gallons under Size
In Now column for FC you entered 10
In Target column you entered 16
In white box to right of that you entered 6

Result should have been 125 oz. - basically almost 1 gallon.

How long after addition - with pump running - are you measuring FC again?
Are you taking the sample from about 18" deep and from the same location as the first sample?
You are using plain old 6% bleach and not the 10% Pool Essentials Walmart product?

Yes to all of above.
Here's a copy paste of the results from the top white window:
1 gallon or 1 (121 oz) jugs
Sample from 18" deep with a 24" piece of 1/2" PVC. Same place.
I checked early this morning. I added the bleach about 7 PM last night and ran it until 11 PM
Plain old WalMart laundry bleach - 6%

 

[mknauss]

Be sure to refresh the webpage. Old data can get carried over.

 

[BillB]

Be sure to refresh the webpage. Old data can get carried over.

Doesn't the "Calculate" button refresh it?
I'm not questioning the data. I can't understand why adding the bleach it tells me to raises the FC so much. It seems illogical but it is happening.

 

[proavia]

Great - just double checking to be sure.

Pool water should be circulated for about 30 minutes prior to taking a test sample. This provides a better gauge of the entire pool.

And add chemicals with pump running too. After adding chemicals, you can grab a sample about 15-30 minutes later if you choose to test then.

Yes, the calculate button should refresh PoolMath.

 

[proavia]

Have you checked to see if acid additions give the expected results? If a measured addition gives a lower pH, your pool volume is set too high.

 

[jblizzle]

Or the bleach is very fresh and extra strong.

 

[BillB]

Great - just double checking to be sure.

Pool water should be circulated for about 30 minutes prior to taking a test sample. This provides a better gauge of the entire pool.

And add chemicals with pump running too. After adding chemicals, you can grab a sample about 15-30 minutes later if you choose to test then.

Yes, the calculate button should refresh PoolMath.

That could be where I went wrong. It had been raining off and on all day. I turned the pump on about 7 PM and took the sample about 5 minutes later. Maybe the true reading would have been greater than 10ppm. That's the only thing I can think of.
Thanks for your help. I think you found the answer.

 

[BillB]

Have you checked to see if acid additions give the expected results? If a measured addition gives a lower pH, your pool volume is set too high.

Acid additions are fine.
I'm certain of the volume.

 

[BillB]

Or the bleach is very fresh and extra strong.

I suppose that's possible. Does that happen with laundry bleach? I would think the makers would be swamped with consumer complaints of people over bleaching their laundry. For the 6% bleach to have done this it would have to have been around 12%.

 

[BillB]

I think I've solved the mystery.
I checked the FC this morning and it was at 14ppm.
PoolMath called for 42 oz of bleach to bring it to 16ppm.
I added it, waited 30 minutes and checked it again. I tested 21 ppm.
That's the same kind of thing I've been getting- way too high.
I kept testing and noticed that the angle I held the R-0871 bottle made a marked difference in the size of the drops that came from it.
I found that if I held it perfectly vertical and gently squeezed I would read 16ppm. If I held it at an angle I would read in the 20s.
It's at 16 now. I'll top it off at 16ppm tonight and test it 30 minutes later before I turn the pump off.
I'll bet I don't have any more problem.
Lesson learned- Hold the drop bottle vertical.

 

[jblizzle]

Yes, that is the way you are supposed to add drops.