Phosphates.....are they worth removing??

[Swampwoman]

Matt, will you consult on the observatory too? I have serious reservations about hacking a big hole in the barn-peaked roof and putting a dome on top all the while living in Michigan where snow load and ice dams makes even a skylight a bad plan. I would rather we construct a balcony-style platform at the front of the pool house with a walkout to a dome but that limits the north view, or so I am told

In other news, I was looking up the instructions, etc. of Orenda PR and comparing same to Seaklear for heavy duty phosphate removal. Virgin territory for me.

I found this video, obviously produced by Seaklear...but it made me wonder a bit: SeaKlear Phosphate Removal Video - YouTube. The masked bottle they're using as the "competitor" is the Orenda bottle. If its remotely true/accurate, there is definitely a difference in seaklears capacity to remove.

In Orenda's detail about removal, they seem to rely heavily on their enzyme product to convert phosphates to ortho and hence what feels like a bit of elaborate and multi-week chicanery to package multiple products into the process. I'm not quite comfortable with that approach, though it might be germane.

It may turn out their method is more meaningful, but I'm going to go the simpler route with a gallon of SeaKlear and 12 ounces of clarifier. That would or should remove roughly 15,000 - 18,000 ppb in my pool it seems, which for my purposes, would be enough to get me under the po4 scaling factor ChemGeek had calculated for me regarding the salt cell. If the process is relatively painless, I might do a second gallon.

I'm still a week or two out from the mad plan, so let me know if any of you have thought processes or opinions about either product. My goal is not zero or even low phosphates...it is simply future salt cell health/operational efficiency.

 

[Saturn94]

At what level does it become an issue for SWCGs?

Having a SWCG and using Jack's Magic Purple stuff, this is of interest to me.

 

[JoyfulNoise]

I think you'd be better off with a raised platform preferably with concrete pillars sunk deep into the ground to hold it up and stabilize it. You'd want maybe 6-10ft of elevation to get you off the ground and an open field for good exposure to the sky. Then just make sure the telescope is bolted to the platform and let it stabilize to evening air temperatures for a good hour or so. I'd even add on a wireless GoPro camera and mount for remote viewing but you'll also need a motorized gimbal with remote control GoTo technology for star-finding. Building an observatory in the barn is not such a good idea for any number of reasons...you really need a dedicated space for the telescope to get good, vibration-free images.

As far as the Orenda versus SeaKlear thing goes, I think either is fine for residential use. SeaKlear removes ~9000ppb per 10,000gal per quart and Orenda is about 10,000ppb. So the difference, in my opinion, is minimal. I agree that the Orenda process is more complicated because they are trying to convert organic phosphates into inorganic phosphates through enzyme action. I'm sure it works great in their lab but I have my doubts how it would work in a real pool. Enzyme processes are very tricky to get working as they typically require very strict pH limits and temperature. Not to mention chlorine can easily degrade or destroy enzymes so I'm not sure how you use their product without dropping your FC level and causing a potential algae mess. It is true that pools will have both organic and inorganic phosphates and that both are capable of being used by algae and bacteria for nutrient supply. I just don't see the benefit in trying to tackle both. Get rid of the inorganic stuff first and then see what happens to the organic phosphates. It is possible for organic phosphates to break down (slowly) and leave inorganic phosphates behind so I'd rather just rely on that happening then trying to muck around with enzymes.

In your case, it is quite clear where your phosphates have come from - regular sequestrant use. Therefore, the best thing for you to do is to just go for the orthophosphate treatment. I don't know that anyone has ever documented calcium phosphate deposition inside an SWG but I have no reason to doubt chem geek's chemistry on that. It would be a neat thing to see....but don't feel like you have to sacrifice your new SWG for the pursuit of science

If I were in your shoes, I'd probably try to do the removal in two steps just to make sure everything is working right. It's not a certainty that you need clarifiers to help your sand filter clear the particulates formed. In fact, I might be worried that you'd add clarifier and then send your filter pressure through the roof necessitating a backwash BEFORE the conversion of lanthanum carbonate to lanthanum phosphate is completed. Even if the conversion happens quickly enough, you could easily try adding 1/2 cup of DE to the filter first instead of clarifier to help with filtration. Then, if that doesn't clear it up to your liking, you can go with the clarifier.

There's definitely a lot of variables here to play with so please keep copious notes so we can all learn from it. Your's would be the most "extreme" version of phosphate removal but a very edifying one because many, many people use sequestrants and probably have very high phosphate levels from them.

As an aside, I just got my Taylor K-1106 test kit in the mail and so I will now set about testing my fill water and pool water for phosphates. I'm fairly certain my fill water is not a huge a source of orthophosphates but I'd like to know what the levels are for certain.

Good luck....and hopefully your husband doesn't bring down the barn roof on his head cutting a hole in it

Matt

 

[AUSpool]

Phosphate removal is a broad spectrum approach. Lack of nutrients affects all living things. Unlike borates which are effective algaecides only against certain types of algae (and really only at levels up near 80ppm), phosphate removal starves ALL biological pathogens of a primary nutrient needed for life.

Mustard algae can be difficult to treat with a sanitizer BUT, like all living creatures, it can not reproduce if basic nutrients are deficient.

To put a figure on it I have always thought of the limiting concentration for microbial growth as being less than 0.03ppm(30ppb), my limnology book, Dodson 2005, suggests that some lakes can have concentrations from 0.08ppm to as low as 0.001ppm. From experience with aquariums I've always found it very problemmatic testing phosphates that low as it is used or recycled through a food web faster than it is made available for a test kit to measure.

 

[MarianParoo]

As an aside, (and please don't bypass Auspool's comment!) Matt: why did you choose the 1106 over the 8005?

EDIT: Never mind. The 8005 seems to need the colorimeter...

 

[JoyfulNoise]

To put a figure on it I have always thought of the limiting concentration for microbial growth as being less than 0.03ppm(30ppb), my limnology book, Dodson 2005, suggests that some lakes can have concentrations from 0.08ppm to as low as 0.001ppm. From experience with aquariums I've always found it very problemmatic testing phosphates that low as it is used or recycled through a food web faster than it is made available for a test kit to measure.

The issue isn't really limiting concentration because that number has little value - humans can "survive" on 6% O2 in breathable air but will be neither conscious not functional until the concentration gets much closer to 18%.

So what is really important is not the limiting concentration but the effect of [PO4] on growth rate. The reason being is that the FC/CYA ratio is predicated on the concentration of active chlorine (HOCl) that is able to kill off algae faster than it can grow. In nutrient-rich waters where the limiting factor for growth is sun light and temperature, the algae doubling times are somewhere between 4-6 hours. Therefore, the concentration of chlorine needs to be matched to the CT kill times such that the kill rate (usually measured in the number of logarithmic reductions, eg, 3-log reduction or 99.9%) is faster than the reproduction rate.

Unfortunately there is not much data I can find on how [PO4] affects the reproduction rate when it is the limiting nutrient but we do know the somewhere below 1000ppb, there is a reduction in growth rates. It is at these levels where the FC/CYA ratio can be lowered since less chlorine is needed to keep the algae in check.

 

[JoyfulNoise]

As an aside, (and please don't bypass Auspool's comment!) Matt: why did you choose the 1106 over the 8005?

EDIT: Never mind. The 8005 seems to need the colorimeter...

Yeah, if I could only afford Taylor's $3,000 UV-VIS Spectrometer I'd be all set!!

The 1106 will have to be good enough for now

 

[Swampwoman]

@Saturn94, this is the (perhaps very speculative) calculation for "possible" phosphate scaling, which also depends on your calcium, water temp, ph per ChemGeek -- this information was discussed entirely because I was nervous about switching to swg with such very high phosphates, and if I did switch, which I will, I wanted to ensure I was operating in a condition optimized for trouble free FC production

pHc = (11.755 - log(CaH) - log(PO4) - 2log(t)) / 0.65
So solving for phosphate level we have:
PO4 = 10^[11.755 - log(CaH) - 2log(t) - (0.65 * pH)]
So for 375 ppm CH, 7.5 pH and 80ºF (26.67ºC) we have
10^[11.755 - log(375) - 2log(26.67) - (0.65 * 7.5)] = 28.44 ppm = 28,440 ppb phosphate

In my pool, with low calcium, at a known 25 ppm or 25,000 ppb, ChemGeek solved for calcium and assumed the higher ph that is in the immediate cell itself where the production occurs, which is way higher than in the pool...so with such high phosphates even at 75 pm calcium and at 8.5 in the cell in theory i could have a problem:

As Matt pointed out, you need rather high calcium AND phosphate levels to get significant precipitation, though in an SWCG cell the pH is higher so the phosphate level is higher as a result. This post gives the best formula for predicting calcium phosphate scaling. If I assume 25,000 ppb phosphate and solve for calcium hardness I get the following and I'll use 30ºC (86ºF) tempertaure and 7.5 and 8.5 pH:

pHc = (11.755 - log(ppm CaH) - log(ppm PO4) - 2log(ºC)) / 0.65
CaH = 10^[11.755 - log(ppm PO4) - 2log(ºC) - (0.65 * pH)]
CaH = 10^[11.755 - log(25) - 2log(30) - (0.65 * 7.5)] = 337 ppm
CaH = 10^[11.755 - log(25) - 2log(30) - (0.65 * 8.5)] = 75 ppm

In the reading I've done of pool tec literature to date (not necessarily accurate ) I've not come across a specific, accurate-sounding level at which phosphates interfere...more just observations that when a cell isn't seeming to output the expected FC, that reducing phosphates has appeared to remedy.

I think in general, If your salt cell plate looks clean on periodic inspection and is producing chlorine as expected, you're fine, although some say phosphate scale is mor difficult to detect visually. If it scales so badly you need to acid bath it to clean it up, and you have high phosphates, and the output doesnt seem right, then removal might be in order

While Jacks purple is phosphonic, the literature ALSO says it contains something to clean your salt cell, and that its been formulated for same. So. Suspect you're golden, though you could always ask them. The fact its formulated for salt tells me they're quite aware of the outlier phenom of phosphate scaling

 

[Swampwoman]

One mor interesting note -- my pool is now almost entirely soft water, AND we run the pump continually for the heater and debris collection, so I've not had any issue. But this article in Aqua magazine had an interesting case of phosphate scale on a heater where "safe" MA was being used...you guessed it, the MA had a phosphonic corrosion inhibitor in it:
The Case of the Mysterious Pool Deposits - AQUA Magazine

 

[Patrick_B]

That's an interesting read SW, as CaPo4 scaling happens to be a subject near and dear to my livelihood. I'm not at all surprised to see them finding deposition in a HX like that. It's just about gauranteed under the right conditions.

 

[Swampwoman]

^yes, I thought it was. When I read it, it contributed to accepting my h's theory that continual running of the heater was both better for the gas bill and oddly in some ways better for equipment longevity -- in my case, anyway
Because I have a vinyl liner, soft water, and ergo very low calcium, I suspect I get away with a lot in terms of the high phosphates. Which is why I'm quick to qualify that just because I control reactive water with FC:cya alone, that doesn't mean that there aren't conditions where truly high phosphates (eg high calcium pools w/swg) aren't problematic.

 

[Saturn94]

@Saturn94, this is the (perhaps very speculative) calculation for "possible" phosphate scaling, which also depends on your calcium, water temp, ph per ChemGeek -- this information was discussed entirely because I was nervous about switching to swg with such very high phosphates, and if I did switch, which I will, I wanted to ensure I was operating in a condition optimized for trouble free FC production



In my pool, with low calcium, at a known 25 ppm or 25,000 ppb, ChemGeek solved for calcium and assumed the higher ph that is in the immediate cell itself where the production occurs, which is way higher than in the pool...so with such high phosphates even at 75 pm calcium and at 8.5 in the cell in theory i could have a problem:



In the reading I've done of pool tec literature to date (not necessarily accurate ) I've not come across a specific, accurate-sounding level at which phosphates interfere...more just observations that when a cell isn't seeming to output the expected FC, that reducing phosphates has appeared to remedy.

I think in general, If your salt cell plate looks clean on periodic inspection and is producing chlorine as expected, you're fine, although some say phosphate scale is mor difficult to detect visually. If it scales so badly you need to acid bath it to clean it up, and you have high phosphates, and the output doesnt seem right, then removal might be in order

While Jacks purple is phosphonic, the literature ALSO says it contains something to clean your salt cell, and that its been formulated for same. So. Suspect you're golden, though you could always ask them. The fact its formulated for salt tells me they're quite aware of the outlier phenom of phosphate scaling

Thanks for the response. So far I've not had any issues with the salt cell. It's rare that I find any deposits on the cell plates.

I should mention that up until a couple seasons ago, I always added a quart of phosphate remover at closing (it came with the closing kit I use to use). I have to wonder if this helped keep phosphates in check. I stopped using it because it makes a mess to clean up at spring opening (a PITA). Also, the conventional wisdom in the forums is that phosphates are irrelevant in a properly maintained pool. Now that I no longer add it at closing, could there be enough buildup to cause future problems? Was this a factor in the unexpected appearance of algae on the wall last August? It would have been helpful if I had tested and kept track of phosphate levels to see what impact my change in closing procedure may have had.

This spring I plan to start measuring and keeping track of phosphates, perhaps as an experiment if for nothing else.

 

[JoyfulNoise]

Thanks for the response. So far I've not had any issues with the salt cell. It's rare that I find any deposits on the cell plates.

I should mention that up until a couple seasons ago, I always added a quart of phosphate remover at closing (it came with the closing kit I use to use). I have to wonder if this helped keep phosphates in check. I stopped using it because it makes a mess to clean up at spring opening (a PITA). Also, the conventional wisdom in the forums is that phosphates are irrelevant in a properly maintained pool. Now that I no longer add it at closing, could there be enough buildup to cause future problems? Was this a factor in the unexpected appearance of algae on the wall last August? It would have been helpful if I had tested and kept track of phosphate levels to see what impact my change in closing procedure may have had.

This spring I plan to start measuring and keeping track of phosphates, perhaps as an experiment if for nothing else.

Great!! Keep good notes and share your observations. The more real-world pool info we have, the better we can do to combat speculation & hype. We serve our membership best by doing honest evaluations of real data.

 

[Swampwoman]

Saturn, I will also be logging this spring for te sake of posterity. While I don't buy the phosphate hype per se, I also don't have enough hard data to refute interference.

My thinking on removal -- not having done it yet -- is to open early and cold, treat for a week (or in my case 2 at this high level) before turning he heater on, then test once a month and see what te level gets to by Oct. if I feel a need to treat again, I'll treat a week before close in order to backwash thoroughly.

I have no idea if lanathum chloride can gum up a heater or not, but I don't really want to find out I am also curious as to whether or not lanathum chloride has an ideal water temp efficacy. I will see if I can find anything out.

What kind of mess did your treatments make on closing previously?

 

[Swampwoman]

One more Aqua article that I dug up -- if you read it, be sure to also read the comments as well that address the wide variance of anecdotal "evidence" about what PO4 level might or might not be too high for problems with salt cells.

The article cites MFGs are recognizing over 500 ppb (so I'm 50,000 x too high but a pool tech notes he regularly has no problem with SWG units on 3,000 ppb of PO4.

Failing Salt Generators: The Phosphate Connection - AQUA Magazine

 

[Saturn94]

Saturn, I will also be logging this spring for te sake of posterity. While I don't buy the phosphate hype per se, I also don't have enough hard data to refute interference.

My thinking on removal -- not having done it yet -- is to open early and cold, treat for a week (or in my case 2 at this high level) before turning he heater on, then test once a month and see what te level gets to by Oct. if I feel a need to treat again, I'll treat a week before close in order to backwash thoroughly.

I have no idea if lanathum chloride can gum up a heater or not, but I don't really want to find out I am also curious as to whether or not lanathum chloride has an ideal water temp efficacy. I will see if I can find anything out.

What kind of mess did your treatments make on closing previously?

I also don't think phosphates are a big deal generally. However, it's apparent to me from conversations on the subject that there are situations when phosphate removal may be a useful tool.

When I've added phosphate remover at closing the water quickly became very milky/cloudy. Over the winter the precipitate would settle to the bottom of the pool and the water turned clear again. At spring opening, I would have to vacuum 2 or 3 times. The sediment stirs up easily so when vacuuming the water quickly clouded up. It also quickly clogs the DE filter, requiring a couple of back washes. Generally it would take a few days running the pump/filter 24/7 to completely clear the water.

Without the phosphate removal process, spring startup/cleaning is much easier/quicker.

 

[Saturn94]

One more Aqua article that I dug up -- if you read it, be sure to also read the comments as well that address the wide variance of anecdotal "evidence" about what PO4 level might or might not be too high for problems with salt cells.

The article cites MFGs are recognizing over 500 ppb (so I'm 50,000 x too high but a pool tech notes he regularly has no problem with SWG units on 3,000 ppb of PO4.

Failing Salt Generators: The Phosphate Connection - AQUA Magazine

Interesting article, which switches the focus of possible high phosphate issues from algae control, the primary focus here, to proper SWCG function (I don't recall that being discussed on TFP).

I am somewhat puzzled about the comment in the article about SWCG manufacturers acknowledging issues with levels over 500ppb. I check the latest version of the owners manual for my Aqua Rite, certainly one of the big boys in the industry, and there's no mention of phosphates anywhere. There is mention of high nitrogen, products like Yellow Out, and dry acid products causing issues.

I'd be willing to bet my phosphate level is well over 500ppb. However, I've not noticed an issue with my SWCG. The last cell lasted 7 years, which is pretty good from my understanding.

 

[JoyfulNoise]

So my K-1106 arrived and I tested both my source (fill) water and my pool water -

Fill Water: [PO4] < 50ppb *

Pool Water: [PO4] ~ 1000ppb **

* Too hard to differentiate 0ppb from 50ppb on color card so I just called it "less than 50ppb" to be safe.

** Previous measurements with Hach test powder showed ~ 750ppb while K-1106 shows a color definitely darker than 500ppb but ever-so-slightly lighter than 1000ppb. For treatment purposes, I will call it 1000ppb.

So that info is good because it means my water has no significant source of [PO4] coming into it except for environmental accumulation (breakdown of organic phosphates into orthophosphate). As well, it roughly means my water accumulates ~250ppb or less per season based on water age.

So, when I treat my water, I should be able to get it close to zero phosphates for the season and not have to worry about accumulating phosphates as I try to lower my FC/CYA ratio. I will test monthly to keep my records accurate and hopefully correlate or rule-out any problems that arise to phosphate levels. If I only have to treat once per year, then my 32oz bottle of SeaKlear (~$40) is going to last 3 to 4 years at least.

 

[AUSpool]

I think your very brave to offer up your pool to the algae gods in the name of science.

...
Unfortunately there is not much data I can find on how [PO4] affects the reproduction rate when it is the limiting nutrient but we do know the somewhere below 1000ppb, there is a reduction in growth rates. It is at these levels where the FC/CYA ratio can be lowered since less chlorine is needed to keep the algae in check.

My old ~1000 page microbiology book devotes only one sentence to phosphorus, "... is required by the cell primarily for synthesis of nucleic acids and phospholipids", although it does describe a bunch of phosphate related processes from cell wall transport to energy transport via ATP.

I think limiting PO4 can be used as a biological control agent but as mentioned it's not a sanitising agent and won't kill the algae. I'm thinking that 1000ppb and even 30ppb of PO4 is too high to be a limiting nutrient. Even at 0ppb population growth would be in the stationary phase where growth = death. Individual cells would die but not because of a phosphate deficiency, the nutrients released when they die would be quickly used by new cells.

My microbial ecology text states that phosphate does limit microbial growth and indirectly offers a concentration / growth rate relationship in the form of nitrogen and phosphate microbial biodegradation of oil in sea water;
At P=0(M) and N=0(M) conversion (%) = ~5%.
At P=0(M) and N=0.01(M) conversion (%) = ~10%.
At P=0.00007(M) and N=0.01(M) conversion (%) = ~55%.
At P=0.00035(M) and N=0.01(M) conversion (%) = ~70%
At P=0.0007(M) and N=0.01(M) conversion (%) = ~75%
At P=0.0007(M) and N=0.005(M) conversion (%) = ~65%
At P=0.0007(M) and N=0.003(M) conversion (%) = ~40%
At P=0.0007(M) and N=0(M) conversion (%) = ~10%



The conversion and hence growth never actually gets to zero.
From Atlas and Bartha, 1972, Biotechnology and Bioengineering, in Atlas and Bartha, 1998, Microbial Ecology.

I'm not sure there is likely to be a usable relationship between PO4 and the FC/CYA ratio and if there was its more likely to be a relationship between a combination of phosphates and nitrates both at 0ppb and the FC/CYA ratio. I've read many requests for help from folks that have uncontrollable algae problems with a zero reading for phosphate. Given that they have an algae issue they do have a nutrient issue, there is just no free phosphate to be detected by a test kit.

Going back to the OP, phosphates and are they worth removing? I think that if your going to test for something you need a reason to test for it and have a set of target values in mind to apply the result to. It seems clear that a high level of phosphate can adversely affect equipment but I'm not sure about biological control in a sanitised pool. I had thought about reducing phosphates for winterising a pool.

I couldn't find anything to do with acceptable levels for public or bather health. In the history of my pool I've had the phosphates tested four times at 320ppb, 0ppb, 30ppb and recently at 0ppb again. Dilution is the solution for me. My LPS recommends a target range of 0-200ppb but don't say why. I'm pretty confident that even with a PO4 result of 0ppb I would have a bright green pool in no time if I turned my SWG off. I was sure my water utility would have a published result for PO4 but nothing, they don't appear to test for it. They have an NO3 level at 0.77mg/L (~770ppb) which when using the redfield ratio would put my tap water phosphate at around 48ppb.

I hope I've been of use, these big books are doing my head in, it's time for swim and a cold beer!

 

[Leebo]

Thank you greatly for your comments Steve. I'll likely have another question or two after I re-read your thoughts, but for now this comment jumps out to me.

I had thought about reducing phosphates for winterising a pool.

Can you expand on that?? Could there be a benefit using a phosphate remover over the winter???