SWG not producing more chlorine when I crank it up

[Bart]

This is my second season with the (newly built) pool. Last year I had my SWG set to 35-40% or so and had good chlorine numbers (1-1.5 or so) and clear water. This year my chlorine numbers have been between .5 and 1.0 and each time I get a reading like that, I bump up my SWG run time, but the chlorine numbers don't seem to change. Here are some numbers:

Salt percentage - 3.3

June 3 - SWG 40% - FC 1
June 10 -SWG 45% - FC 1
June 17 -SWG 55% - FC 1
June 23 -SWG 65% - FC 1
July 1 - SWG 80% - FC 1
July 9 - SWG 80% - FC .5
July 12 - SWG 85% - FC .5

Other numbers from last weekend:

ph 7.5
T/A 90
CH 550
CYA 80

Pump run time - was 12 hours, now 13 hours.

Any idea what's going on here? I'm more than double than I was last year and I'm not maintaining the same levels of chlorine.

One other data point - during one of my low chlorine spells, I did a shock with bleach, but I don't think I turned the SWG off. Could this have ruined the cell?

Thanks!
Bart

 

[JasonLion]

You probably have a low level algae problem. You should do an over night FC loss test, which will most likely indicate a need to shock the pool.

 

[Bart]

I don't understand. Would algae in the pool prevent the SWG from working properly?

Also, if I shock with bleach, I need to turn off the SWG, correct? How long do I need to leave it off?

Thanks!

 

[elwood58]

I could make a few possible assumptions based on your test results, and other comments included in your post.

1. Your CH is on the high side, which could contribute to scaling on the Salt Cell in your SWG. I would at least do a cleaning of the cell.
2. You do not list CC in your test results, but I assume it may be higher than 1, and means you may have organics developing that will eat all of your chlorine.
3. I assume your run time is primarily during daylight hours? If not, the time you choose to test FC will be important.
4. I assume your salt reading is in ppt and not ppm, so 3300, which should keep most cells happy.

As far as turning the SWG off during shock, I do it to save cell life and electricity, but am not under the impression that it would actually harm my cell. It is just redundant in the face of shock levels of FC.

 

[Bart]

Thanks elwood!

I had a massive scale problem when I opened the pool and beat it back with 2 no-drain acid washes. Do you think that could be a factor here? Did the scale get removed from the pool, but not the SWG itself?

Thanks again,
Bart