Is my SWG Cell dead?

[run53]

Stats from TF-100:

CYA=55 (slowly getting it up to 70)
pH=7.6
TA=75
CH=180
FC=4.0-7.0 (using BBB since SWG failing)
CC = 0.0 - 0.5
salt 3200

SWG = mybluepool with SCC-25 cell
installed May, 2007
run 10-12 hours per day from May 1 thru Oct 1 since May 2007.
cleaned cell every opening with 10 to 1 ratio of water/muriatic acid.
Looks clean now.

currently running the cell at 80% (past years I would run it at 50% and bump to 65% in hot weather) but continue to lose about 2ppm of FC each day (in 80-90 degree heat and lot's of sun) so I have been adding bleach to keep FC up. I also noticed that the pH stays pretty constant whereas normally with the SWG, I need to add muriatic acid once a week.


I suspect that the cell is bad, given the age, but how do I know for sure? I don't want to spend $500 for a new cell if that is not the problem. So, how do I know it's not the control unit or something else? It would seem that if the cell is not working, I would have high voltage and low amps. But how and where do I take these measurements and what are the normal values I should expect? I am pretty sure i can just take a voltage reading across the leads going to the cell but not sure how to measure the Amps unless I build a series connection (amps is measured in-line??) to the cell. There is nothing in my SWG documentation about output in terms of voltage amps or Chlorine output.

Any expert help would be appreciated.

 

[Bama Rambler]

Have you ran an OCLT to make sure it's not something that's eating the FC? I suspect it may be the cell, but an OCLT is a good place to start.

There have been several brands of units private labeled by mybluepool over the years, so I don't know which one you have. Maybe a resilence branded one. ???

 

[run53]

Have you ran an OCLT to make sure it's not something that's eating the FC? I suspect it may be the cell, but an OCLT is a good place to start.

There have been several brands of units private labeled by mybluepool over the years, so I don't know which one you have. Maybe a resilence branded one. ???

OCLT varies but is always either 0.5 or 1.0 FC loss overnight. According to the OCLT document, that should be ok.

Perhaps the next simplest test is to take a reading directly from a return while the SWG is running (boost). I have an adapter that fits into a return and can direct the flow into a collector. If the FC reading is more than the pool FC, I can assume the SWG is making chlorine.

If it makes chlorine, then the next question would be, how much is it generating?
If I knew that my OCLT is 0.5 and if I run the SWG overnight, I should be able to convert the rise in FC to a Chlorine generation rate. Is there a formula for this?

For Example:
SWG set to 100% for 12 hours
OCLT = 0.5
FC at 7:00pm = 4.0
FC at 7:00am (next morning) = 7.5
pool size = 24000 gal

Chlorine output from SWG = 4.0ppm in 12 hours at 100%

How can I convert 4.0ppm to lbs/24hr ???

 

[Bama Rambler]

That's a lot easier than you think. Use the Pool Calc and enter the first number as the Now number and the second test as the Target number and then switch the chlorine type cell to chlorine gas and it will give you how many oz of gas it would take to get there and then just do the math to go from the number of hours between the tests to extrapolate it for a day. I.E. if you produced 6 oz of chlorine in 12 hours then multiply that by 2 to get the number of oz in 24 hours. 6*2=12 oz per day.

 

[run53]

That's a lot easier than you think. Use the Pool Calc and enter the first number as the Now number and the second test as the Target number and then switch the chlorine type cell to chlorine gas and it will give you how many oz of gas it would take to get there and then just do the math to go from the number of hours between the tests to extrapolate it for a day. I.E. if you produced 6 oz of chlorine in 12 hours then multiply that by 2 to get the number of oz in 24 hours. 6*2=12 oz per day.

Very cool. I didn't know that the chlorine type cell in the calculator had chlorine gas a a choice.

I will run this test overnight at 100% to see how much chlorine is generated. I found out that my cell should generate at a rate of 1.38lbs/24hr. So I now have something to compare it to. The result won't be exact due to variation in OCLT but I will have a good ballpark figure of how much it's generating (if anything) versus the expected output.

Thanks!

 

[run53]

OK, I've completed 2 tests and now I'm still not sure what is going on. Here is what I did.....

last night at 6:30pm TC=7.5, FC=7.0

Turned SWG to 100% for overnight ( 12 hours)

This morning at 6:30am TC=9.0, FC=8.5

Assuming an overnight FC loss of 0.5, the SWG generated 2.0ppm at 100% over 12 hours.

Using the Poolcalculator, at 24,000 gallons, the SWG generated 6.4oz of FC in 12 hours, for a rate of about 12.8 oz/24 hours. It's supposed to be rated at 22.08oz/24hr (1.38lbs/24hour).

Also, I took a reading from the nearest return (attached a connector hose to get sample coming from the return), while it was still operating at 100% and at 6:30am and measured TC=10.5, FC=10.0. Recall at 6:30am pool reading was TC=9.0, FC=8.5.

So, the SWG is definitely making chlorine. However, it is either being eaten up by something in the water, or it's not generating at the rate it should be. I will do another OCLT tonight to see what my overnight loss is. When I did it 2 times last week, it was 0.5 and 1.0 loss. Seemed reasonable.

Would appreciate further comments on my trouble shooting methods. Especially if i have miscalculated something.

Will report back the results of OCLT tomorrow. If I am losing more than 0.5-1.0 of FC, then i will know the answer. If not, then I guess my cell is slowly dying as opposed to not working at all. Is this typical of cell failure?

 

[JasonLion]

Yes, it is typical for older cells to loose "strength" towards the end before they wear out completely.

 

[run53]

Last nights OCLT was not good.
went from FC=7.5 to FC=5.5

2.0ppm loss.
I suspect the SWG dying probably left the FC at below minimum recently and now have some minor organics eating FC.

Sounds like it's time to shock.

Of course it's a Saturday and everyone wants to use the pool. Is it ok to shock and swim? Or best to wait for Monday when everyone is back to work?

The water is pretty clear, although not as crystal clear as it usually is.

 

[run53]

Actually if i re-do the calculations from the 100% output SWG overnight test assuming a 2ppm FC loss (see previous post above), then the SWG output was 11 oz for 12 hours at 100% (24k gallons). This is exactly what it is rated at. Looks like the salt cell is good after all and my problem was organics eating FC faster than the cell is capable of making it.

I've decided to shock tomorrow night since the pool will be used this weekend. I will just keep the FC levels in the 7-8 range until then to keep it as it is.

I just changed my DE and when I opened up the filter, the smell was a little foul. Definitely some organics going on in the pool.

 

[TrentonTom]

Will a dead cell give a false salt level reading? Salt reading is 1900 on my Aqua Trol but I can tell by the taste of the water that the level is closer to 3000. Where in the SWG is the salt level detected? I have a new cell reeady to install in either case but was just curious as to how the salt concentration is calculated. Thanks.

 

[RobbieH]

I don't trust the salt content numbers on my system, even after calibrating it. I still just trust the drop test.

IIRC, a failing cell will give false readings.

 

[TrentonTom]

Will the SWG generate if the level displayed (1900) is below the recommended range (2700-3400)? Or does the displayed level dictate whether the generater starts to produce chlorine?