I don't think that cya is even that critical. As long as you're above 60 ppm and below 100 ppm you sould be fine. At least that's what the local health department wants on my commercial pools. May be splitting hairs here a little, so to speak :|
I don't think that cya is that critical
- Thread starter kiksroks
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Re: CYA Testing
kiksroks,
The CYA level is very important (though I agree that +/- 10 isn't a big deal) because the amount of "active" disinfecting, algae inhibiting and oxidizing chlorine (that is, hypochlorous acid) is not dependent on the Free Chlorine (FC) level alone, but rather on the ratio of FC to CYA. If you don't worry about the CYA level, then you can end up using too little FC and get algae growth. This can be avoided if you are using a supplemental algaecide (PolyQuat 60, phosphate remover, Borates, etc.), but if you are using chlorine alone which is most economical, then to ensure not getting algae a manually dosed pool needs a minimum FC that is roughly 7.5% of the CYA level while an SWG pool needs a minimum FC that is roughly 5% of the CYA level.
The chemistry behind this fact is described here and has been known since at least 1974 when the equilibrium constants for the chlorinated isocyanurates (that is, chlorine bound to CYA) were definitively determined. I apologize for the industry that has, for whatever reason, withheld important chemical information from pool operators/servicers such as yourself as well as from consumers of residential pools. I am just a residential pool owner with no ties to the industry. One example of incorrect information that is taught is the classic graph of chlorine vs. pH that really only applies when no CYA is in the water. The classic graph and the correct graph when CYA is present are shown here.
Are you running your commercial pools without any algaecide and with FC levels that are less than 5% of the CYA level -- so below 5 ppm FC when the CYA is at 100 ppm? Do you get any algae in those pools? You might just be lucky in having water very low in phosphates or nitrates (algae nutrients). We have seen quite a few SWG pools with the "SWG manufacturer recommended" 1-3 ppm FC levels at 60-80 ppm CYA get algae, usually with 1-2 ppm FC or with 3 ppm FC and 80 ppm CYA.
Richard
kiksroks,
The CYA level is very important (though I agree that +/- 10 isn't a big deal) because the amount of "active" disinfecting, algae inhibiting and oxidizing chlorine (that is, hypochlorous acid) is not dependent on the Free Chlorine (FC) level alone, but rather on the ratio of FC to CYA. If you don't worry about the CYA level, then you can end up using too little FC and get algae growth. This can be avoided if you are using a supplemental algaecide (PolyQuat 60, phosphate remover, Borates, etc.), but if you are using chlorine alone which is most economical, then to ensure not getting algae a manually dosed pool needs a minimum FC that is roughly 7.5% of the CYA level while an SWG pool needs a minimum FC that is roughly 5% of the CYA level.
The chemistry behind this fact is described here and has been known since at least 1974 when the equilibrium constants for the chlorinated isocyanurates (that is, chlorine bound to CYA) were definitively determined. I apologize for the industry that has, for whatever reason, withheld important chemical information from pool operators/servicers such as yourself as well as from consumers of residential pools. I am just a residential pool owner with no ties to the industry. One example of incorrect information that is taught is the classic graph of chlorine vs. pH that really only applies when no CYA is in the water. The classic graph and the correct graph when CYA is present are shown here.
Are you running your commercial pools without any algaecide and with FC levels that are less than 5% of the CYA level -- so below 5 ppm FC when the CYA is at 100 ppm? Do you get any algae in those pools? You might just be lucky in having water very low in phosphates or nitrates (algae nutrients). We have seen quite a few SWG pools with the "SWG manufacturer recommended" 1-3 ppm FC levels at 60-80 ppm CYA get algae, usually with 1-2 ppm FC or with 3 ppm FC and 80 ppm CYA.
Richard
Re: CYA Testing
My commercial pools are running 60-80ppm cya and 1-3 fc. They are tested monthly for cya and daily for fc. They do not need any other algaecides or phosphate removers. I charge 3 times the amount for these pools as I do residential and they get a visit twice a week rather than once for these reasons. If for some reason I need to use other than liquid chlor I won't hesitate to use di-chlor but obviosly I cannot on a regular basis.
I have seen very few properly maintained swg pools with any algae what so ever(even with water temps in the upper 80's to low 90's. We usually get the cya level up to about 80ppm and then check/adjust only when we need to check/add salt or we aren't producing enough fc and need to figure out why.. Generally our swg pools run constant 3.0ppm fc.
I do love the salt water chlorine generators!
My commercial pools are running 60-80ppm cya and 1-3 fc. They are tested monthly for cya and daily for fc. They do not need any other algaecides or phosphate removers. I charge 3 times the amount for these pools as I do residential and they get a visit twice a week rather than once for these reasons. If for some reason I need to use other than liquid chlor I won't hesitate to use di-chlor but obviosly I cannot on a regular basis.
I have seen very few properly maintained swg pools with any algae what so ever(even with water temps in the upper 80's to low 90's. We usually get the cya level up to about 80ppm and then check/adjust only when we need to check/add salt or we aren't producing enough fc and need to figure out why.. Generally our swg pools run constant 3.0ppm fc.
I do love the salt water chlorine generators!
Re: CYA Testing
So in the commercial pools with daily FC testing, I presume that is local staff and they also add some chlorine as well? Then your twice a week visit is for things like brushing the pool and verifying that things are done properly? It is surprising to have the lower end of the FC range with the higher CYA level and not have any algae in any of those pools. With only once a week visits to residential pools, do your customers have to add more chlorine? If so, are they all using Trichlor for continuous feeding or do they add other sources regularly?
The SWG pools at 3 ppm FC with 80 ppm CYA is on the edge, but given the magic water you apparently have it's perfectly fine. Well now I can see why you don't see any sort of chlorine/CYA relationship because you can run your commercial pools as low as 1 or 2 ppm FC with 60-80 ppm CYA and not see algae developing. Perhaps just lucky with low phosphates or nitrates or something else inhibiting algae growth. It's certainly not the experience of many residential users nor Ben Powell's experience with his commercial pools nor others I've spoken with (at the NEHA conference I recently attended, most commercial/public pools had much higher FC levels almost all above 3 ppm and some above 5 ppm and this was done both for algae prevention and to have a sufficient chlorine buffer for peak bather loads).
[EDIT] If there is high bather load in the commercial pools, then perhaps they have CC, specifically monochloramine, since that can be effective at killing or inhibiting algae. That could explain why these pools are able to tolerate a lower FC level than the low bather load residential pools. It's at least a possibility and a little more scientific than magic water! [END-EDIT]
Richard
So in the commercial pools with daily FC testing, I presume that is local staff and they also add some chlorine as well? Then your twice a week visit is for things like brushing the pool and verifying that things are done properly? It is surprising to have the lower end of the FC range with the higher CYA level and not have any algae in any of those pools. With only once a week visits to residential pools, do your customers have to add more chlorine? If so, are they all using Trichlor for continuous feeding or do they add other sources regularly?
The SWG pools at 3 ppm FC with 80 ppm CYA is on the edge, but given the magic water you apparently have it's perfectly fine. Well now I can see why you don't see any sort of chlorine/CYA relationship because you can run your commercial pools as low as 1 or 2 ppm FC with 60-80 ppm CYA and not see algae developing. Perhaps just lucky with low phosphates or nitrates or something else inhibiting algae growth. It's certainly not the experience of many residential users nor Ben Powell's experience with his commercial pools nor others I've spoken with (at the NEHA conference I recently attended, most commercial/public pools had much higher FC levels almost all above 3 ppm and some above 5 ppm and this was done both for algae prevention and to have a sufficient chlorine buffer for peak bather loads).
[EDIT] If there is high bather load in the commercial pools, then perhaps they have CC, specifically monochloramine, since that can be effective at killing or inhibiting algae. That could explain why these pools are able to tolerate a lower FC level than the low bather load residential pools. It's at least a possibility and a little more scientific than magic water! [END-EDIT]
Richard
I just noticed an inconsistency that might explain the experience kiksroks wrote about in this thread. In this post in this thread, kiksroks says that his pools are running 60-80 ppm CYA with 1-3 ppm FC. However, in this post he says that his pools are maintained at 3-5 ppm FC instead of 1-3 ppm FC. The 3-5 ppm FC with 60-80 ppm CYA is on the edge of algae prevention, but is certainly better explained than 1-3 ppm FC. The recommendations in the chlorine/CYA chart in the Pool School are based on conservative levels that prevent green algae in virtually all pools, even those with excellent algae growth conditions (such as plenty of nitrates and phosphates nutrients and ample sunlight).
Richard
Richard
If the pool is getting shocked regularly, commercial pools generally are, and the FC level is reasonably uniform (either a SWG or an automated chlorine feed of some other kind), then it makes sense to me that lower FC levels work acceptably. It is not uncommon for a pool with CYA around 80 and FC around 1 to go a couple of weeks without getting algae. If the pool is shocked the algae level goes down to zero. You then have another couple of weeks before obvious problems would be expected.
Thanks. I didn't even think about shocking as he hadn't mentioned that. A weekly shock would tend to kill off algae and it takes several days for it to reproduce enough to become a problem and that's with no chlorine. So at low chlorine levels, I can see how you might get by for a week until the next shock levels wipe out what's grown. Nevertheless, this thread on the Pinellas County pool study showed many pools even without chlorine and with high bacterial accounts with no green algae (though yellow/mustard and especially black algae was reported in a lot of pools). I had suspected algaecides that could have been used, but it could just be that they shock weekly, but let the chlorine get too low during the week -- so bacteria grow, but green algae doesn't take hold.
Anyway, I'm always on the lookout for exceptions or for explanations of unusual results.
Richard
Anyway, I'm always on the lookout for exceptions or for explanations of unusual results.
Richard
That makes alot of sense. It also jives with the "recommendations" that many receive to "shock your pool every 2 weeks or more depending on weather and bather load" and why many people are able to go quite a while with this type of routine before the problem becomes uncontrolable (CYA climbs to a point of no return 
) and their old methods no longer work.
) and their old methods no longer work.