Numbers Not Making Sense?

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H

HowardL

0
Apr 19, 2011
74
First, a confession. After taking over the pool in April, I used all of the help here on the board to get everything balanced nicely. Maybe a little too nicely, as I soon settled into a routine where I made slight adjustments automatically to my chlorine withour everyday testing. I simply used the prior changes to guide my additions of approximately the correct amount of chlorine. Now, in June, we have steady 90s degree weather and the pool temp is about 88. In my short cut, I failed to consider that much warmer water combined with full and strong sun would change the rate of chlorine usage.

However, I am now paying the price for this laziness as I noticed a couple small green spots in the pool while brushing it 2 days ago. Algae! I probably wouldn't have even noticed the small spots if I wasn't brushing and regularly looking things over. I took a quick reading and had FC and CC both at 1, while pH was up to 8. I added a full gallon of Menrad's 12% liquid chlorine (given my 30,000 gallon pool should have moved the FC up very considerably), added muriatic acid, and hoped it didn't get too much worse over night. I should note that the water has remained clear throughout as I think i reeally did catch this very early.

Yesterday I brushed again as things looked to be improving (many of the green spots were now grayish black and began to brush away) and I anxiously awaited sundown to retest levels. Here's what I got....
Temp =85
FC = 2.5
CC = 0.5
pH = 7.2
TA = 90
CH = 280
CYA = 70

Again, based upon my pool and a desire to knock this bad boy out, I used the Pool Calculator and saw that shock level would be 20, given my situation. Basically, as I read the Calculator, I again needed to add another 12% gallon. I added it last evening and looked forward to what today would bring.

Bright and early today I examined the pool. Water still clear, green spots mostly faded, but a scattered few remain. Then I did my water tests. Here's what I got...
FC = 6.5
CC = 0
pH = 7.4

I am having very mixed feelings. First, I am glad that I am getting a "0" reading on my CC, but given the fact that I still have a few green spots I question this. I also question why my FC would only be at 6.5 when I'm thinking it should be at least in the teens.

Am I doing the tests wrong? Is there a way to check this? I know that I have stubbed my toe a few times trying to use the Calculator so maybe my inputs or conclusions are wrong from the caluculator. Otherwise, could my liquid chlorine have degraded in potency while being stored? Not sure where I go from here, other than to keep brushing and get a few gallons of standard 6% bleach and see if it makes a difference. Any thoughts, comments or suggestions appreciated. Thanks.

Howard
 
You are doing everything correctly, you just need to add more chlorine. There is relatively little algae, so this won't be so difficult to recover from, but you still need to shock the pool properly, and that means adding more chlorine to bring FC back up to shock level as needed.

It is possible that the chlorine is not as strong as it is listed, it is also quite possible that you lost that much chlorine fighting the algae you had. Algae uses up chlorine, way of the world.

Algae plus chlorine doesn't always create CC, so nothing unusual there.
 
You still have something lurking consuming the chlorine. You need to raise it up to shock level this evening, say around 7 or 8 pm. Then at 10pm, test the FC. Then test again in the morning, before the sun hits the pool. If you lose more than 1ppm of chlorine overnight, you are not done shocking the pool.

I also suggest using the shock level from the CYA chart (see my sig). And in the future - keep the FC above the "min" at all times by testing daily or every other day - no more assumptions lol :)

Enter in your test result in the "now" box, and the goal shock level in the "target" box. Make sure you have the correct % strength chosen, along with the correct jug size. Hit calculate and it will tell you how much chlorine to add. IF you aren't sure you are calculating correctly post what you come up with and we can verify it for you.
 
Adding to what Jason said, your chlorine dosage calculations are w-a-a-a-y off. To move a 30k pool from 2.5ppm to 20ppm requires almost 9 gallons of Clorox.

Post back if you can't figure out the pool calc....it is a required tool.
 
First, thanks so much for the prompt help. I just was out brushing again and the water looks great. A few spots (roughly the size of a pea) remain widely scattered with the biggest remaining area around the rim of an underwater pool light.

Knowing that I am Pool Calulator challenged, I appreciate the pointers. So, I go to the calculator re-input the numbers and figure out my biggest error. I was calculating with the pool size still on 10,000 gallons....So I actually needed to put in 3x what I was doing. Now the recommendation is to add 840oz of 6% bleach. 840/128 = approximately 6.5 gallons. I will add this evening and report back in the morning. Thanks again.

Howard
 
Hey, Howard, sorry I missed the 12% but it looks like you weren't bothered by my error and are now well on your way.

I'll bet keeping your FC at the correct level is all you needed for a sparkling pool the rest of the summer.
 
OK. Added 9 x 96oz jugs of 6% bleach (864 oz) about an hour ago. Thunderstorms bearing down on us so I just did a quick test...
FC now = 21.5.
43 drops of solution is a lot of drops, but we have achieved shock!

I will test again in morning but 1 quick question. With thunderstorms won't that dilute my chlorine numbers and make the overnight test a little iffy? Comments welcome. Thanks.

Howard
 
HowardL said:
I will test again in morning but 1 quick question. With thunderstorms won't that dilute my chlorine numbers and make the overnight test a little iffy?
Click to expand...
Correct, don't rely on the overnight test if there are thunderstorms that add a lot of water and/or debris.
 
OK, so we had steady rain/thunderstorms all night. Still raining now. A bit of debris in pool but not much. Here are my 7am readings:
FC = 14
CC = 0.5
pH = 7.4
I'd love to go out and brush the pool, but standing outside in a thunderstorm holding a metal pole dipped into the water doesn't strike me as a great idea. Don't need the Pool Calculator to figure that one out.

Where do I go from here? Thanks.

Howard
 

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Just had a short break in the storms so I got the pool brushed, emptied skimmer baskets, and backwashed. Also added another 96oz of bleach that I had around. Figured no harm since I'm probably going to have to go back to the store and get another few jugs anyway.

Since it's still so overcast and dark outside, hard to say much about the water other than still clear. No or very very little visible algae spots as pretty much anything that was green has turned brownish grey...and there wasn't much of that to start with. Any suggestions or comments welcomed. Thanks.

Howard
 
Since your FC fell by about 8ppm overnight, you still have organics (algae) in the pool even though you cannot see them.

You should continue to complete the shock process until....
1. Your water is crystal clear.
2. You lose less than 1.0 FC during the FC overnight loss test
3. Your CC's test is .5 or less
 
Well it does look like you lost quite a bit of FC overnight, but if the water is clear, go ahead and keep it at shock level today (for good measure) and perform the overnight FC loss test tonight. If you pass, you're done :goodjob:

edit: or what Dave said :lol:
 
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