Chlorine levels in swg pool


New member
Sep 4, 2009
Hi everybody,
First I’d like to say this is an awesome forum and it has helped me maintain an awesome pool so far…I haven’t posted any questions yet because I always find answers by simply searching. But today I couldn’t really find anything that fit exactly.
I live in League city, TX (Houston). I have an 8 month old diamond brite plaster pool that is aprox 15,000 gallons. I have all Pentair equipment with an IC 20 swg chlorinator. Since the summer started I have been running it at 100%. We usually swim in it on the weekends for about 4 to 6 hours total.
I have the TF-100 test kit and test my pool on a weekly basis. Typically PH is high at about 8 to 8.2 ( new plaster I assume) but most measurements are in line so I’ve just been adding about a pint of acid per week and that’ll bring it in line. Alkalinity is about 80 every test and as I add acid it seems to fall back to about 60 to 70. I have a spa that’s spills over into the pool, which can also be contributing to the weekly jump in ph.
FC levels are typically between 4 and 6 which I have considered normal with CYA level of 50 to 60, which I’m thinking I may need to bring to 70-80. Once in a while I’ll get a CC test of .5, which has not bothered me.
Calcium hardness is typically between 210 and 250 and I have not worried about that.
Water temperature has been hovering at about 86 to 90 degrees as it’s been getting really hot here. Oh, and we've had lots of rain lately.
I run my pool 12 hour per day with a pump RPM of about 2000. I left it at 2400 all last week by mistake.
For the last three tests my FC has been only 3 ppm with no CC’s even though I have the chlorinator at 100%....Soooo my question is: Should I be worried? Should I add liquid chlorine to boost it up? Should I raise my CYA level? The water looks AWESOME, super clear, but I want to avoid a problem before it starts…
Her are today’s test results, I’ve already added some acid to bring PH down…
FC- 3
CC – 0
PH – 8.2
T/A – 70
CH – 220
CYA – 50
Temp – 87 degrees
Also, I have added CYA in powered form before by dumping it in the skimmers, is that the best way or will it hurt my equipment?
Thanks in advance for your help,


New member
Sep 4, 2009
Oh, I forgot to mention that salt level is good at 3400 ppm's and chlorinator seems to be working just fine.


LifeTime Supporter
Nov 12, 2009
Indialantic, FL
I would raise the CYA to at least 70.

I have the Pentair IC-40 with a 16K gallon pool - with CYA at 40 I had to run at 60%. Raised the CYA to 70 and was able to lower the SWG duty cycle to 25%.


Jun 28, 2010
Palm Harbor, FL
+1 on PoolMom's advice. I just went through this "unseen organics" issue. Actually, I've had it every summer since I got the pool. The advice from this group saved my sanity and my pool. I could run my SWG at 100% and barely get to 2ppm FC. Pool store guys kept telling me to add stabilizer (wrong!). Follow the advice here. Get a FAS/DPD test kit so you can accurately test your FC and CC. Don't trust the pool store. Do the overnight test. When I first tested mine I lost 5ppm FC in about an hour!

I just turned my SWG down again, from 40% to 30% as my FC is still rising. My water is crystal clear. It took a week of shocking, brushing, and testing, but now that it's over everything is perfect.

Good luck
Mike M.


New member
Sep 4, 2009
Thx everybody. Yes, I do have a dpd fas test. I tested last night and again this morning. Loss was what I thought negligible, less than .5 (still six drops in the pink solution to get it to clear), so I think I'm okay there. I got some liquid conditioner to get it up to 70 quickly. I poured it in this morning, we'll see what happens. One thing I haven't done is acid wash the cell, so I may do that too.
Thx again for the replies!
Thread starter Other Threads of Interest Forum Replies Date
W Spas and Hot Tubs 2
E Just Getting Started 5
T Algae - Prevention and Treatment 2

Other Threads of Interest