IC40

[mark46143]

Split from another thread for better visibility.

There have been a few pool users who reported seeing algae when their SWG pools were at 2 ppm FC so I would say that 3.2 ppm FC is closer to the correct number in the 70 ppm CYA range (though doing things like regular brushing might help one run at a lower FC level since the main problem is for algae stuck to surfaces that don't pass through the SWG cell to get superchlorinated and killed). There are even some SWG users where even 3 ppm was not enough, but that was for mustard/yellow algae (if I recall correctly). Because of the variety of factors that affect algae growth, including temperature and nutrient (phosphate, nitrate) levels, any recommendation is going to be something that works in most, but not all, situations. Ben's original chart was his "best guess" based on experience and knowledge and works for almost every pool for green algae prevention (mustard/yellow algae prevention needs closer to his Max column to prevent). I just translated such experience into consistent chemistry based on what is known about the disinfecting chlorine level at various FC and CYA levels.

The Pentair recommendation probably comes from the pool industry "standard" recommendation of 1-3 ppm FC that more recently has been changed to 2-3 ppm FC (I think -- could be 2-5) as the recommended range, but that standard says nothing about chlorine as a function of CYA. A new standard is apparently being developed (see this link), but I doubt that it will be any better regarding any discussion of Free Chlorine relative to CYA as the industry continues to point to the Pinellas study (that I discuss in this thread) as to why CYA doesn't matter.

You are welcome to try 2 ppm FC and let us know if your pool remains crystal clear, but with algae the recommendation has to be based on the chlorine level relative to CYA that has virtually all pools be free of algae. If some pools can operate with less chlorine, that's nice, but not useful as a general guideline.

Richard

OK, so last year definitely had some organics going in the pool did the shock treatment many times, drained water to get CYA down from 120's, etc, etc.

This year, Pool has been open about 30 days, Intellchlor 40 is running at level 5 and my FC is 2.5, no CC, CYA 70, PH 7.4, total alk 180 (little high). That is the readings from my test kit.

Pool water is 83. Pool water clarity is great, no visible signs of issues around the pool, no debris, etc. The lights were left out over the winter and there's no debris coming off the housing when I brush them (unlike last year).

Up until late last year I ran the IC 40 at 3 and never had a problem. I have taken off the IC 40 and it is producing chlorine (foams).

Thoughts here? Im pretty shocked that this pool is not holding chlorine.

Thanks

 

[Richard320]

Re: Chlorine/CYA Chart

OK, so last year definitely had some organics going in the pool did the shock treatment many times, drained water to get CYA down from 120's, etc, etc.

This year, Pool has been open about 30 days, Intellchlor 40 is running at level 5 and my FC is 2.5, no CC, CYA 70, PH 7.4, total alk 180 (little high). That is the readings from my test kit.

Pool water is 83. Pool water clarity is great, no visible signs of issues around the pool, no debris, etc. The lights were left out over the winter and there's no debris coming off the housing when I brush them (unlike last year).

Up until late last year I ran the IC 40 at 3 and never had a problem. I have taken off the IC 40 and it is producing chlorine (foams).

Thoughts here? Im pretty shocked that this pool is not holding chlorine.

Thanks

An overnight loss test will tell you if there's anything growing in the pool.

Maybe the SWG is just showing age?

 

[mark46143]

Re: Chlorine/CYA Chart

Richard, Thanks. I checked before posting. The IC 40 was new last year. I took it out and ran it in the a bucket of water and it just bubbled like crazy with chlorine.

 

[jblizzle]

But the OCLT will confirm if there is something living in the pool consuming the FC as fast as the SWG is producing it.

 

[chem geek]

An FC of 2.5 with a CYA of 70 ppm is not enough to prevent green or black algae growth if there are sufficient nutrients (phosphates and nitrates) in the pool. So you may just have nascent not-yet-visible algae growth and the SWG is having a hard time keeping up with this extra chlorine demand so you have to set it up to a higher on-time. An overnight chlorine loss test may help you see if you've got some extra chlorine demand. The solution would be to SLAM the pool to kill off the algae and then to set a higher FC target that is closer to the recommended 3.5 ppm FC at your CYA level (or from Pool School rounded to 4 ppm).

The change from last year might be that you've got more algae nutrients in the water, perhaps from over the winter. I'm not sure why your pH isn't rising given your high TA level (do you have automatic acid addition?).

The IC 40 produces up to 1.4 pounds of chlorine per 24 hours so in your 30,000 gallon pool that would be only 5.6 ppm FC over 24 hours or 0.23 ppm per hour. By "level" do you mean how many LEDs are on where level 3 was 60% and level 5 is 100%? If you are only running your pump for 8 hours a day, then that is only (8/24)*5.6 = 1.9 ppm FC per day which is about normal. Basically, you have an undersized SWCG for your pool. We normally recommend getting one about twice (or more) the "recommended" manufacturer size since they woefully underestimate what is really needed.

Does your pool get more sun this year than last year? Or did you use a cover last year but not this year? That can make a difference as well.

 

[mark46143]

Chem Geek,

Thanks for the reply. I have another post on here (not sure how to look it up) but, I think (based on what I was told by my pool guy which is a TFP supporter) that the issue I have is behind the liner. The The liner is 2 years old, shortly after installation, the liner got tears from the automatic pool cover. While the tear was repaired water probably got behind the pool. You can visibly see growth on a seam (about 1 meter in length). You can't brush it off so it may very well be behind the liner.

As for the IC 40, it runs 24 hrs a day at 2350 rpm.

We have/are slamming the pool. The discoloration has improved somewhat but, it's still there.

Have you ever successfully solved this problem without "replacing" the liner? I was wandering if we took the liner out of the track could we introduce some algaecide or something else - either in dry form or a slurry for that section.

Pool water looks great. I have a feeling that the issue is behind the liner. There are no other visible signs (lights, steps, etc).

Any thoughts here?