Trouble Maintaining FC in SWG Pool


New member
Jul 2, 2020
Hello! I am a new pool owner and new to this site! I am not sure who else to ask as my local pool store is probably quite sick of me by now lol. In short: my issue is constantly dropping FC levels despite all other normal tests (salt, CYA, etc) and increasing from 40% to 70% with multiple rounds of shocking. How I do I know what is wrong with my cell? I'm suspecting user error (lol) bc all my lights on the cell are green and when I turn on "superchlorinate" the FC jumps up dramatically.

More background if it helps:
We moved into this house (in FL, in case that matters) in the middle of May. We kept all the previous owners settings (40%, 8h run time) and did no maintenance of the pool for 2 weeks (no tests, no chemicals, no cleaning). In that time, there was constant direct sunlight on the pool during the day, no rain, and high bather load (husband and I went in daily and had ~10 person pool party). We got it tested after 2 weeks and all tests were 100% normal (FC 3.0). Then we got 2 weeks of torrential rain and actually had to drain the pool a bit. All the tests were off then and we added CYA, salt, and shocked the pool. Thought we were back in the clear as everything normalized. But FC kept dropping. We shocked again and increased percentage to 60%. Back to zero. Now, we basically are either shocking or running "superchlorinate" for 24h once a week to keep it clear. This has been ongoing for all of June.

From Tuesday to Wednesday this week: we ran 24h "superchlorinate" and got level from 0.5 to 4.5 at 1 pm on Wednesday (with home test). After 1 pm, pool ran until 6 pm at 70%. Started again today at 10 am, again at 70%. Tested at 1 pm today and was 2.0. I just feel like it is dropping so fast for such a high percentage!

The pool store says we need to increase run time to 10 h but the previous owner said he always keeps it at 10-6 pm for the past 10 years lol. And we personally had a solid 2 weeks of sun + high bather load that was maintaining perfectly at 8h run time and 40%. I would be inclined to just buy a new cell but "superchlorinate" seems to work, indicating it should be working yes??

Other tests recently done: CC 0, pH 7.4, TA 80, CH 395, CYA 60, Salt 3400, no phosphates. I have already cleaned the cell and had a technician come out to look at it and he said it looks fine.

If anyone has any suggestions i would greatly appreciate it! Thank you!


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

I doubt that there is anything wrong with your cell.. It is you... :mrgreen:

I suspect you have an algae bloom, even though it is not visible yet.. This is because your FC got way below the required levels in the saltwater section of this chart... FC/CYA Chart

You need to quit going to the pool store and just start testing you own pool water..

I'm pretty sure if you ran a Overnight Chlorine Loss Test or OCLT that you would fail.. Indicating an algae bloom. The only way to get rid of algae is to perform a SLAM... SLAM Process

I know I threw a lot of stuff at you, so take your time and read through our Pool School.. Pool School - Trouble Free Pool And see what we are all about.

If you follow our process you will never have to go back to the pool $tore again, and will never have to add a single bag of ""shock" ever again.

I assume you have the IntelliChlor, most likely the IC40, is that correct??


Jim R.


New member
Jul 2, 2020

Thank you so much for your response!! I appreciate your help! Lol yes user error as suspected o_O I think this makes perfect sense - for some reason, I just wasn't believing I could still have algae after adding 2.5 gallons of chlorine.. lol I see now the required levels to SLAM are much higher!!

Yes, we have the IC40! I will start the SLAM after more testing supplies come in - we have the Taylor 2006 kit but running low on the chlorine reagents after using them a lot this month! We are at 7.4 pH now, is it necessary to lower to 7.2? We have the IntellipH and I'm not sure how to lower the pH other than just adding the muriatic acid straight the pool.

I also wanted to ask, are we safe to swim in it for now as long as we can keep the FC to 2-5 w the "superchlorinate"? I don't love the idea of swimming in algae lol but we do have a long weekend coming up here.. any potential long-term side effects?? Of note, the pool is not green or cloudy at all! Not like super-crisp like it is after the chlorine is added but def not what I would call cloudy!

Thanks again for your help!! Feeling so relieved just to have a plan :D


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
IF (big if) your CYA is really 60, you can swim in chlorine up into the 20s with no problem. At 60 CYA it should never dip below 3. I would say try to keep it above 5 if there's a lot of swimmers, even if that means you have to add bleach manually. FC/CYA Chart