Pool School Question

[tucsontico]

According to the Pool School article "Water Balance for SWGs," the best time to run the SWG is:

"...during the day while the sun is shining on the pool. Unless there is some other reason not to run the pump during the day, like time of day electric rates that are higher during the day, program the pump to run while the sun is shining on the pool."

My question is, simply,: Why?

I currently run my in-floor cleaner from 8 PM to 12 AM and the filter from 12:01 AM until 4 AM for a total of 8 hours. My SWG is only on with the in-floor cleaner, so I'm "chlorinating" for 4 hours per evening. Seems a bit counter-intuitive to me to run the SWG during the day. From what I understand, even with a proper CYA of 70-80 ppm, running the SWG while the sun is out will burn off chlorine almost as fast as your SWG is adding it to the pool.

Thanks in advance!

BTW, today's K-2006 test results:

FC- 3.0
CC- 0
pH- 7.8
TA- 110
CH- 225
CYA- 60
Salt- 3400
Borate- 0
Temp- 76ºF

 

[Isaac-1]

You don't want your FC levels to drop below certain minimums, so it makes sense that you want to generate your chlorine during the period that is is being burned off the fastest to keep the chances of dropping below the minimal values the highest. If your SWG can barely keep up with the sunlight burn off rate then there is no way that it could produce enough chlorine for your pool during a 4 hour nightly run.

Ike

 

[Casey]

And you are 1ppm below the recommended FC level for a CYA level of 60 (for SWG). Just saying...

 

[tucsontico]

You don't want your FC levels to drop below certain minimums, so it makes sense that you want to generate your chlorine during the period that is is being burned off the fastest to keep the chances of dropping below the minimal values the highest. If your SWG can barely keep up with the sunlight burn off rate then there is no way that it could produce enough chlorine for your pool during a 4 hour nightly run.

Ike

Ike,

Thanks for the explanation. That makes sense. However, I've never tested my SWG to see if it will keep up to the sunlight burn off rate. I assume that the Intellichlor IC40 will more than adequately produce enough chlorine to handle the all day, full sun that lands on my pool. I'll swap my cleaner/filter schedule to the daylight hours next week to test the SWG capability.

 

[tucsontico]

And you are 1ppm below the recommended FC level for a CYA level of 60 (for SWG). Just saying...

Casey,

You're correct. We had a strong windstorm (25-35 mph winds all day) yesterday. There's a bit more debris in my pool than usual. I've not had a chance to clear all the debris. I also didnt increase the SWG output to compensate for the extra organic material decay until tonight. Should be back to proper FC levels tomorrow!

 

[chem geek]

[EDIT] edited calculation to show more details [END-EDIT]

According to the Intellichlor® brochure, the IC40 produces up to 1.40 pounds of chlorine in 24 hours. So 4 hours would be ((4 hours)/(24 hours/day)) * (1.40 pounds chlorine / day) * (16 ounces/pound) = 3.73 ounces weight of chlorine over 4 hours. In 20,000 gallons that's 1.4 ppm FC. That seems like a low chlorine demand for Arizona and I'd expect a higher chlorine loss as we move towards summer. You might even need to move your CYA up to 80 ppm with a slightly higher FC target to lose somewhat less chlorine.

 

[Casey]

Casey,

You're correct. We had a strong windstorm (25-35 mph winds all day) yesterday. There's a bit more debris in my pool than usual. I've not had a chance to clear all the debris. I also didnt increase the SWG output to compensate for the extra organic material decay until tonight. Should be back to proper FC levels tomorrow!

The joys of early Spring! :lol: Very few people have their covers off right now and I get an occasional reaming and rubbing from my family for having my cover off but I know who's not going to be green with envy in a few weeks!

 

[tucsontico]

The joys of early Spring! :lol: Very few people have their covers off right now and I get an occasional reaming and rubbing from my family for having my cover off but I know who's not going to be green with envy in a few weeks!

Yep! Here in Tucson my water temp is rising about 2ºF per day with the solar (bubble) cover on. Gonna be 90ºF today so I'm taking off the cover and, possibly, swimming a lap or two in the 78º F water!

 

[tucsontico]

According to the Intellichlor® brochure, the IC40 produces up to 1.40 pounds of chlorine in 24 hours. So 4 hours would be (4/24)*1.40*16 = 3.73 ounces weight of chlorine. In 20,000 gallons that's 1.4 ppm FC. That seems like a low chlorine demand for Arizona and I'd expect a higher chlorine loss as we move towards summer. You might even need to move your CYA up to 80 ppm with a slightly higher FC target to lose somewhat less chlorine.

Chem geeK,

Thanks for the expert calculations! Presently, I have a solar cover (bubble wrap-style) on my pool and that is helping with chlorine retention. (Obviously, it helps decrease evaporation losses, too.) I am taking that off this weekend and will be rescheduling my SWG to run in the daylight hours. Since it has been only 1 week with my SWG, I'm still learning the pools chlorine requirements. The temps are now running about 90ºF each day so I'm going to have to increase the SWG output anyway. Thanks again!

 

[tucsontico]

Took the solar cover off and brushed/skimmed the debris from the pool. Test results:

FC- 4.0
CC- 0
pH- 7.8
TA- 110
CH-225
CYA- 60
Salt- 3400
Temp- 79º F

Here's a couple of pictures:

Cover on:


Cover off:


BTW, the water is so clear I can read the imprinted manufacturer's name on my main drain! The TFP method works!

 

[PharmerAnthony]

Nice pool and desertscaping.

 

[tucsontico]

Nice pool and desertscaping.

Thanks! We really enjoy the space and the "oasis" feel.

 

[timerguy]

Chem geek, I'm reluctant to question an expert, but what does the *16 designate in your formula? I'm used to using a production percentage, but that's clearly not what that is.

 

[jblizzle]

Pounds to ounces ... don't feel silly

 

[timerguy]

boy do I feel silly! But that brings up another question-- does that mean it's running at 100% the whole 4 hrs? Btw Jason,I tried to answer you're pm to me the other day, but your storage is/was full.

 

[chem geek]

I've edited my post to show the calculation details more clearly.

 

[timerguy]

Thanks cg. I guess intelliflos run at 100% by default.

 

[tucsontico]

Thanks cg. I guess intelliflos run at 100% by default.

Actually, the IntelliChlor, when coupled with an EasyTouch or IntelliTouch control panel, can be set from 20% to 100% in 1% increments. Otherwise it jumps in 20% increments when using the built-in controls on the IntelliChlor. According to Pentair, this means is the SWG is only running for x% of the time it is powered on and senses sufficient flow through the cell.

Mine is currently set for 75% so using a 4 hour run time and chem geek's calculation, my SWG is only producing 3.73*.75=2.89 ounces (by weight) of chlorine. However, since I removed the solar blanket, I've increased the run time to 6 hours at 75%. Again using chem geek's formula my SWG is now producing about 4.2 ounces of chlorine. I haven't tested the pool today but will post the numbers when I get them.