Will Phosphates increase chlorine demand?

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chem geek

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Mar 28, 2007
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San Rafael, CA USA
I have had over 3000 ppb phosphates in my pool and was able to recover from having 0 ppm FC in the past by shocking as described in ping's post or the Pool School (in fact, I've had bacteria convert CYA into ammonia creating a huge chlorine demand). There's one user on this forum with over 18,000 ppb phosphate and is able to manage the pool with chlorine alone. A service tech often doesn't have the time, but this site and its methods are for pool owners that don't just visit their pools once a week. Basically, if you get behind and algae is growing vigorously, you have to shock the pool with chlorine -- there's no way one can just superchlorinate (i.e. run at 100%) with the SWG cell and have any hope of keeping up, BUT once one kills off the algae one can have the SWG keep up if the FC is high enough for the CYA level.

We've had thousands of SWG pool owners come on the forum with pools in various states of phosphate level, algae, etc. and they are all able to have green algae killed off and the pools subsequently maintained even with high phosphate levels. Again, phosphate removers should be seen like algaecides -- like insurance -- so if someone wants to prevent problems that can occur if the FC level drops due to some spike in chlorine demand, then there are extra cost options such as phosphate removers or algaecides. It's up to the pool owner to decide which route they want to go. Most on this forum choose to simply maintain the FC for their CYA level, shock only for unusual situations, and not use other products at extra cost (except sometimes borates, mostly for other reasons such as extra pH buffering and sparkle to the water).
 

linen

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Jul 30, 2010
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swimcmp said:
If chlorine is 0 and I do mean 0, it doesn't make a bit of difference if cya is 1 or 100. This is what we have seen first hand. Phosphates over 2000 and unable to get a chlorine reading, once phosphates are lowered then we can get a chlorine reading, and then it makes the difference where the cya level is.
The fact that the FC level got to 0 in the first place is the problem. Then algae is likely, even more so with high phosphate levels. If the FC never got below the appropriate normal minimum for the pools cya level, then phosphate levels of 1 or 100 or 1000, etc. does not matter.

We may be seeing this from two different angles. Most of use seasoned BBB method pool owners (not pool service) diligently keep our FC levels maintained appropriately for our cya level. We ignore phosphates. My guess is you are showing up to a pool that dropped below the proper FC level due to limited visits (business necessity)...then I could see using a phosphate remover in hopes of preventing algae when the FC level is not measured and maintained regularly/daily.
 

swimcmp

In The Industry
Nov 8, 2011
1,091
Moberly,MO
I guess after 30 plus years in the business I know there is always more than one way to view things. But if a customer calls and says they cannot maintain a chlorine reading, I test for phosphates. IF the level of phosphates is above 1500 we use a phosphate remover, getting the levels down then swg maintains a chlorine reading, looks to me there is a relationship to phosphates/chlorine. I know I am not the sharpest knife in the drawer, but past experiences are hard to forget. We started selling salt systems as a way to provide customers with an alternative to high priced chlorine. If the only answer is to throw more expensive chlorine into the pool why sell swg's, defeats the whole idea of the swg. Right?
 

PAGirl

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Jun 5, 2012
2,390
Central PA
swimcmp said:
I guess after 30 plus years in the business I know there is always more than one way to view things. But if a customer calls and says they cannot maintain a chlorine reading, I test for phosphates. IF the level of phosphates is above 1500 we use a phosphate remover, getting the levels down then swg maintains a chlorine reading, looks to me there is a relationship to phosphates/chlorine. I know I am not the sharpest knife in the drawer, but past experiences are hard to forget. We started selling salt systems as a way to provide customers with an alternative to high priced chlorine. If the only answer is to throw more expensive chlorine into the pool why sell swg's, defeats the whole idea of the swg. Right?


What was the CYA level of said pools? What do you do in the pools that can't hold chlorine that don't have elevates phosphates?
 

swimcmp

In The Industry
Nov 8, 2011
1,091
Moberly,MO
I can honestly tell you PAGirl I don't recall seeing a swg pool not maintain chlorine without an elevated phosphate level. CYA means nothing if there is 0 chlorine. I understand the opinion that phosphate doesn't matter. This is all about saving money and maintaining sparkling water as cost effectivly as possible. Alot of the posters here badmouth pool stores, granted some stores deserve that, but don't throw out the baby with the bathwater.

We have been doing pools for 30 years in a retail store, 45 plus years of owning our own. When we bought our first pool I promise you there weren't many places to turn to for answers. We learned alot by trial and error.
 

ping

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Jun 24, 2011
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Long Beach, CA
swimcmp said:
I guess after 30 plus years in the business I know there is always more than one way to view things. But if a customer calls and says they cannot maintain a chlorine reading, I test for phosphates. IF the level of phosphates is above 1500 we use a phosphate remover, getting the levels down then swg maintains a chlorine reading, looks to me there is a relationship to phosphates/chlorine. I know I am not the sharpest knife in the drawer, but past experiences are hard to forget. We started selling salt systems as a way to provide customers with an alternative to high priced chlorine. If the only answer is to throw more expensive chlorine into the pool why sell swg's, defeats the whole idea of the swg. Right?


What I see, there is an algae/chlorine relationship and not a phosphate/chlorine relationship. You need a certain amount of chlorine in the water at all times to kill the algae. If that chlorine level drops and algae starts growing in the pool, you will then need extra chlorine to kill the algae. When algae is in a pool and there is a SWG, it will usually keep the algae from becoming a bloom but it will not keep up the proper amount of chlorine in the pool. Eventually the algae overcomes the SWG and you get the customer calling that the pool can not hold chlorine. Most home owners will not even see any algae in this condition. The problem is that the algae is consuming all of the chlorine that the SWG is producing even though you can not see any algae. If the pool gets overloaded while in this condition then the algae will most likely bloom.

You are seeing a relationship with phosphate/algae because you are taking away a food source for the algae. Without the food source the algae can not multiply and thus keeping it in check. Eventually you will be able to kill enough of the algae off by starving it so it can not multiply and the SWG will catch up. For a pool service this is not that bad of an idea and might be the best way for you to run your service.

The overall cost of a SWG compared to liquid chlorine is about a wash for most home owners. The big difference is the convienence of the SWG. You might be saving money as a pool service because these SWG pools will be easier to maintain as the chlorine and CYA levels will be more consistant. These pools will develop fewer problems if the FC/CYA relationship is correct to start with.

For the home owner using the methods taught here at TFP, testing and having the proper FC/CYA relationship is the way to go. If the home owner does get in trouble with algae then bleach is his friend. Controlling phosphates is just another expense that is not required.
 

Swampwoman

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Apr 27, 2012
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Grand Rapids, MI
Swimchmp, I think Ping has summed it up nicely, but to give you real live anecdotal evidence that there is obviously NOT a "direct" relationship between phosphates and chlorine demand, consider my unusual situation:

I have phosphates in excess of 25,000 ppb right now (NOT a typo, and yes, that's ortho) due to opening/recovering a foreclosure swamp this spring and subsequent heavy weekly use of iron sequestrate (Jack's pink). At opening, I also had ammonia, produced in part by CYA-eating bacteria and 16 wheelbarrows of leaves and anaerobic conditions), and yes, my chlorine zero'd a lot at first. In fact, the pool techs I had hired were mystified, and tried several "shocks" to get a read, but could not.

With the help of these folks at this bulletin board, I was able to completely recover said swamp WITH CHLORINE ALONE. I've also been able to maintain it with chlorine alone, in accordance with the chlorine/cya chart on this board.

I've not had any algae outbreaks, my daily chlorine demand is about 30% (sometimes 40%) of target, and the water is absolutely beautiful. So, IMHO, if there were any relationship whatsoever between chlorine demand and phosphates -- it'd be showing up in MY POOL. And it's not. I'm actually often using less daily chlorine than many others. But I NEVER EVER LET IT DROP. Cause that would be playing with fire, to steal chem geek's analogy ;)

That said, I do intend to splurge on the commercial level of phosphate remover AND polyquat when I close this year because hey, I don't care about the extra money if it helps reduce my opening effort - I'd rather not endure 12 days of "shock and awe" next spring ;)

I hope that gives you good fodder for thought and some clarity about what is possible. At the same time, if it's expedient for your SWG customers to simply starve off the nascent algae that's outstripping their chlorine production by using phosphate remover, well, makes sense to me! I am for solutions, not dogma ;)
 

linen

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Jul 30, 2010
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Twin Cities, MN
swimcmp said:
But if a customer calls and says they cannot maintain a chlorine reading, I test for phosphates.
Just to give you a perspective...if a poster were to tell us they could not maintain chlorine...we would ask for full test results and probably recommend a Overnight chlorine Loss Test. Most often, when they do this, they will post back with a more than 1 ppm FC lose, so we know that they have organics using up their chlorine. THe next step we would then recommend is shocking the pool until they meet the three criteria in the Shocking Process...this is a "sustained superchlorination" approach. If they caught it quick, then this will take a day or two for them to pass the three criteria. Once those are passed, we would recommend that they are more diligent about maintaining their pools above the minimum FC level for their cya level based off the Chlorine/cya chart (or the poolcalculator.com). If they followed the recommendations, then their pool at that point will be clear and remain that way as long as they are diligent about maintaining the appropriate levels.

Not once in this process is a phosphate remover needed or suggested.
 

chem geek

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Mar 28, 2007
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San Rafael, CA USA
One other fact about phosphates is that there are orthophosphates which are what get measured in the phosphate test and are what algae can readily use as an available nutrient and there are organic phosphates that algae can only slowly use. Phosphate removers only remove orthophosphate, not organic phosphates (or inorganic polyphosphates, for that matter). So if a pool is let go with FC getting to 0 ppm, then bacteria can consume the organic phosphates and convert some of them to orthophosphate and algae can take off even in a pool that has measured near 0 ppb phosphates. This isn't that common, but it does happen and explains why some people who have used phosphate removers still can get algae. We get some reporting in to the forum each year.

Phosphate removers are just one tool in the arsenal, as are algicides. You can have your customers maintain a minimum FC that is at least 5% of the CYA level in SWG pools or you can use phosphate removers on any that get algae or are unable to keep up with chlorine demand because you aren't having them maintain such levels and don't shock the pool at an FC appropriate to the CYA level for shocking if they have algae for whatever reason (such as not adjusting the SWG on-time appropriate for the amount of sun and bather load). Phosphate removers are insurance, not the only solution. No one said they never worked to reduce algae growth -- just that they aren't the only way to prevent such algae growth or "invisible" chlorine demand from nascent algae growth.
 

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benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
swimcmp said:
I can honestly tell you PAGirl I don't recall seeing a swg pool not maintain chlorine without an elevated phosphate level.

Swimcmp, I am shocked that you have never seen a pool that cannot maintain chlorine without elevated phosphate levels with the 60-70 customers you say you have. I have one pool, mine, and it will drop to 0 chlorine if not monitored. I have always had low phosphate levels below 125ppb except for recently when I did this ascorbic acid treatment that sparked this thread.

SWCG systems can not be run without supervision. Chlorine levels in a SWCG pool will fluctuate so you have to adjust the chlorine level albeit not that often. I have had many a day where I go test my chlorine and it is running on the low side so I dump one bottle of chlorine in and bump the percentage up (or adjust my on/off time) on the SWCG to maintain. If I test and it is high I bump the percentage down (or again adjust the on/off time). This is how they work.

So if you have customers with SWCG pools that claim they cannot maintain their chlorine levels I would recommend more training for the customer. This training would be on how to be more vigilant and adjust percentages and how make adjustments before it costs you time and them money.
 

swimcmp

In The Industry
Nov 8, 2011
1,091
Moberly,MO
You can lead a horse to water but you can't make em drink. Same goes with teaching a customer how to properly use equipment. I will always believe that there is a connection between phosphates and chlorine. You may believe that it is an organic use of the chlorine but I know what works for us and how it works .
 

benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
swimcmp said:
I will always believe that there is a connection between phosphates and chlorine.

For the benefit of newbies, I have to say that believe what you like, but I would think that if you want to be well rounded in you line of business you would want to gain a COMPLETE understanding of what is going on. That way if confronted by any situation you would have the complete knowledge of how to respond. This is not to say that in your line of business that adding phosphate remover is not the best course of action from a business point of view.

For anyone that doubts that phophates have no effect on chlorine demand, in a properly maintained pool, add phosphate to a perfectly good pool (use 0-20-0 fertilizer) and monitor the result. With a PROPERLY maintained FC for the level of CYA, you will quickly see that nothing will happen with that phosphate in the water. Let the FC drop below that required for you level of CYA and you can expect the wrath of algae.
 

UnderWaterVanya

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Jun 14, 2012
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Mint Hill, NC
swimcmp said:
You may believe that it is an organic use of the chlorine but I know what works for us and how it works .

I think you know what works but not how. Chemistry does not support the model that you believe. It is probably not an important distinction in many cases - but if you understand the chemical WHY then you may be better equipped if a remedy fails and you need to approach it differently.
 

duraleigh

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Apr 1, 2007
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Beating a dead horse now. Swmcmp's position, despite evidence to the contrary, is intractable. I am locking the thread as any further discussion seems pointless.

It probably should have never gotten this far because of the potential confusion it causes many folks who are simply looking to manage their pool water in the most effective, simple and efficient way possible.
 
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