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Phosphates, Phosphate Removers and CuLator™ Metal Remover

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Phosphates and Phosphate Removers

Key Takeaways:

  • Phosphate removers should be seen in the same vein as algaecides.  They inhibit algae growth (by lowering a nutrient level) but may not always stop it completely.  Like algaecides, they are insurance against algae growth in case the chlorine level gets too low.
  • As with algaecides, they are a preventative measure, but are not necessary if the appropriate minimum FC/CYA ratio is maintained as chlorine alone can kill algae faster than it can reproduce.
  • Phosphate removers do not remove organic phosphates that algae can still use, though growth is slower.
  • Phosphate removers should not be used to clear an existing algae bloom since the oxidation of algae will release additional orthophosphate.  Use them after clearing algae from a pool.


Algae needs sunlight, water and nutrients to grow.  The most important nutrients include sources of carbon, nitrogen and phosphorous.  For plants such as algae, the carbon is primarily obtained from carbon dioxide which is always plentiful in pools since pools are intentionally over-carbonated as represented by Total Alkalinity (TA).  The nitrogen is obtained in pools primarily from nitrate though can also come from ammonia or nitrite when chlorine is not present.  The phosphate primarily comes from orthophosphate though some simple organic phosphates can be used with more difficulty (and slower growth).


Nitrates are a by-product of the chlorination of nitrogenous compounds so are relatively plentiful in pools and there is no way to reduce their level other than water dilution.  Phosphates can come from the oxidation of organic matter and also from metal sequestrant products that are based on phosphates though the breakdown of some of these compounds such as HEDP is rather slow.  Both phosphates and nitrates are found in fertilizer and in soil so can get blown or brought into pools.


The inorganic phosphate, known as orthophosphate, can be significantly reduced by adding a phosphate remover which is either lanthanum chloride or lanthanum carbonate.  Lanthanum phosphate is very insoluble so phosphate removers usually get phosphate levels somewhere below 100 ppb which is low enough to significantly inhibit algae growth so long as there are not high levels of organic phosphates.  Initially, it is mostly lanthanum carbonate that is formed and gets caught in the filter.  Then, any phosphate in the water exchanges with the carbonate to form lanthanum phosphate.  Phosphate removers, at a minimum, significantly reduce algae growth rates.


Phosphate removers should be seen in the same vein as algaecides.  They are one of several tools to prevent algae growth.  They are not necessary if one maintains a Free Chlorine (FC) level that is appropriate for the Cyanuric Acid (CYA) level.  If the FC is at least 7.5% of the CYA level in manually dosed chlorine pools or if the FC is at least 5% of the CYA level in saltwater chlorine generator (SWG) pools, then algae growth is prevented using chlorine alone.  Phosphate removers and algaecides are therefore insurance policies if the proper FC/CYA ratio is not maintained for whatever reason or if one wants to use a lower FC/CYA ratio.


CuLator™ Metal Remover

Currently under discussion.

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Replies to This Discussion

I should add that a straight phosphate remover will significantly cloud a pool as lanthanum carbonate and lanthanum phosphate do not clump well.  They will eventually get caught in the filter, but if one is using such a straight product, then using a clarifier will help clear the pool faster.  Some phosphate remover products have a clarifier in them for that very reason.
Great article on phosphates...As a manufacturer and educator of the industry on the subject of phosphates there are a couple points I would like to clarify more fully... While phosphate removers can remove what is classified as one of the primary growth nutrients for algae, a phosphate remover should never be used in place of an algaecide particularly if algae are already present. In cases where there is excessive algae it should be noted that a majority of the nutrient is already in the plant. This is why it is important to kill existing algae by means of chlorination or use of an algaecide. Once the algae has died off orthophosphate will be released back into the pool water which will cause a spike in the phosphate levels when tested. This is the time when phosphate removal becomes crucial to prevent a second occurence of algae after treatment. Also, it should be noted that high levels of phosphate in a chlorine generator pool can be responsible for preventing the unit from producing sufficient FAC to keep up with demand

Yes, that's a good point that with an existing algae bloom that needs to be dealt with on its own first through physical removal and/or oxidation (depending on how extensive the bloom).  I'll add a key takeaway on this point.


It's not true, however, that all of the phosphate will be released back into the pool as orthophosphate.  Some of the organic phosphates in algae material won't get fully oxidized or hydrolyzed to produce orthophosphate, though some will.  Algae vary in their ability to breakdown and utilize organic phosphates; bacteria tend to be able to use organic phosphates more readily.  The phosphatase enzymes have a relatively short half-life, especially in the presence of chlorine, so it's really the living microorganisms that are able to convert organic phosphates to orthophosphate.  It is true that there is an out-of-equilibrium concentration of ATP in cells and that killed cells that release their contents into the bulk pool water will have much of this ATP become hydrolyzed to ADP releasing one orthophosphate rather quickly.  Further hydrolysis to AMP releases an additional orthophosphate though it's not clear how quickly this occurs.  DNA contains lots of phosphate in its backbone, but it is unclear how readily this is released at typical pool chlorine concentrations -- it is more likely to be filtered out especially if a clarifier is used.


As for saltwater chlorine generator (SWG) pools, I'll have to disagree with you since an SWG can absolutely keep up with nascent algae growth if the FC/CYA ratio is high enough.  The problem is that many manufacturers recommend 1-3 ppm FC with 60-80 ppm CYA which is not a high enough of a ratio to prevent algae from growing faster than chlorine can kill it.  This can appear as an increased chlorine demand even when the water is clear (i.e. the algae is not yet visible).  In an SWG pool, an FC that is 5% of the CYA level will kill algae faster than it can reproduce even when the phosphate and other nutrient levels are high, so 3 ppm FC with 60 ppm CYA or 4 ppm FC with 80 ppm CYA.  If there is already chlorine demand from nascent algae growth, then shocking with chlorine can kill it off and then the FC/CYA level maintained appropriately.  There are thousands of SWG pool owners reporting on multiple pool forum sites that are able to maintain the pools algae-free and with normal chlorine demand in spite of some with phosphate levels of 3000 ppb or more.  This is also true for manually dosed pools though the safer minimum FC level is 7.5% of the CYA level in that case, partly due to the inconsistent dosing and partly due to a lack of super-chlorination as occurs in a portion of an SWG cell.


Now it is true that at high algae nutrient levels the pool is very "reactive" and can turn quickly if the chlorine level gets too low.  So phosphate removers should be seen like an insurance policy where even if algae is not completely prevented, it is certainly slowed way down in its growth giving one more time to fix the situation and kill off what starts to grow.  However, like other algaecides, while useful they are not necessary since chlorine at appropriate FC/CYA ratios will kill algae faster than it can grow regardless of nutrient level (ultimately the growth is limited by sunlight and temperature even with plentiful nutrients).

Slightly off the subject as it stands, but, what about sequestering agents that have a phosphonic acid base?  I've read about and encountered pools in which use scale and stain controls have contributed to high phosphate levels.  I'd be curious to hear your thoughts on this subject.

It is true that the metal sequestrants that use phosphonates / phosphonic acid will slowly break down and release orthophosphate.  HEDP is somewhat chlorine-resistant to such breakdown, but it will still break down given enough time.  The non-phosphonate metal sequestrants, such as EDTA, are usually not as good at sequestering metal and they are less chlorine-resistant so often result in a higher chlorine demand.


So one has the choice of using more effective metal sequestrants that eventually release phosphate or less effective ones that have higher chlorine demand but don't release phosphates.  Since phosphates don't matter if one maintains the appropriate FC/CYA ratio, one would normally use the best metal sequestrant such as HEDP and not worry about the phosphates.  If one did worry about phosphates, one could still use a phosphate remover -- I don't believe it to be incompatible with HEDP.


Another alternative is to use a product that physically removes metal from the water.  Some products claim to not only sequester the metal, but to coagulate and capture it in the filter.  I don't know if such products actually work as described.  Another product, CuLator™, claims to capture and remove metals in its packet which is used in the skimmer. (it's an expensive product).  I'm trying this product out right now since I am still living with some rusting mounts for underwater stainless steel bars in my pool when years ago I used Trichlor pucks in a floating feeder that parked itself near such mounts and rusted them.  So I usually have iron ions in my pool.  We'll see if it actually removes these metal ions.  Fortunately, I don't have enough to stain unless the pH gets to 8.0 at which point I can see some yellowing of the plaster in some areas.

I would like to hear more about your use of CuLator, I did use it last year in a hot tub and the cover of the tub blew off , customer was out of town when they came back tub had sand that had blew in and the CuLator had explosed I'am thinking picked up metals from the sand and over loaded it? Has anyone esle had this happen?

I've been monitoring the use of CuLator on several forums and unfortunately it still has mixed results.  It works for some and not for others. In the case you describe, if the CuLator got overloaded, then the bag would probably have been colored.  They say the bag doesn't necessarily get a color, but that seems to be more when there aren't a lot of metals in the water.

Ok I will follow your monitoring of CuLator I have several pools and hot tubs with well water and only had that happen in one tub but I took the other out I didn't want it to happen to other one. So please let us know you finial results, THX

I just had a report of CuLator working, though the bag didn't change color and it took a few weeks.  The pool kept turning green when shocking but after using the CuLator it stopped.  That's not definitive since it might have stopped on its own, but it's something.  Never had a bag explode/burst, though.

very important to understand the subject before you discuss it - algae grows in the dark on the underside of the ice cap in Antartica.  National Georgraphic Jacques Cousteau 1972 expedition

Algae grows in 40 ppm of free chlorine.  The chlorine removes the chlorophyl of simple algae.  Chlorine is a poor algicide and may be a limiting factor as an algistat.  Chlorine is a fantastic disinfectant / sanitizer it shouldn't be used for any other reason in a swimming pool or spa water.  Over dosing with chlorine can only make the situation worse instead of better.  The phosphate removers do not remove anything but drop it to the bottom as salt.  A total waste of money.

The swimming pool industry fills itself with gimmick chemistry and then produces mountains of BS to support the false claims.  Due to the numerous variables and the fact the people are swimming and bathing in it -  the treatment of pool and spa water is an art not a science.  After almost 50 years of treating swimming pools worldwide and reading copious amounts of smoke and mirror data.  I would suggest it is time to get back to reality and treat swimming pool water and spa water using the basics -

Dennis, I totally agree with you on the gimmicks in the pool industry, but in my experience with algae in a pool, chlorine has worked in most cases. There are thousands of different species of algae, with their own particular characteristics, some more resistant to chlorine than others.



I couldn't find anything about algae on the page you linked to about Cousteau's 1972 Antartica expidition.  However, a search of "algae" on that website gave several hits including one on The light zone and the dark zone where they say (bold emphasis mine):


The foundation of life on land is the photosynthetic activity of plant life. Similarly, the foundation of ocean life is the photosynthetic activity of “plants” in the sea: phytoplankton, photosynthetic bacteria and algae. Phytoplankton, comprising almost 95 percent of total marine productivity, live in the top 200 meters (660 feet) of the global ocean, where they find the sunlight needed to photosynthesize.


Also, light does penetrate ice to a certain degree so unless it is under hundreds of feet of ice, algae could still be expected to grow, albeit slowly.  We've seen algae grow in pools under ice during the winter when "let go" (i.e. no longer chlorinated).


Though there are many different species of algae and some are more chlorine-resistant than others, most typical pool algae will not be able to reproduce faster than getting killed in a chlorinated pool when the Free Chlorine (FC) is at least 7.5% of the Cyanuric Acid (CYA) level in manually dosed pools or around an FC of 5% of the CYA level in saltwater chlorine generator (SWG) pools (an exception is yellow/mustard algae that needs an FC of around 15% of the CYA level to prevent growth of an existing outbreak so normally one shocks to completely get rid of this algae).  This has been proven in tens of thousands of (mostly residential) pools.  Now if the CYA level is extraordinarily high, then one can have algae grow at relatively high FC levels, though we've never seen any pool with 40 ppm FC have algae grow.  Now killing off algae already in a large bloom takes higher levels of chlorine since it gets consumed so quickly and the algae can be thickly clumped, but it doesn't take that much to prevent algae growth in an already well-maintained pool.


It is not true that chlorine only removes the chlorophyll of simple algae.  Chlorine is a reasonably powerful chemical that substitutes for hydrogen on some nitrogenous organic sites and oxidizes ammonia and some organics as well including amino acids, proteins and DNA.  Its destructive powers inside algae (as well as bacteria) are not simply limited to chlorophyll alone.  Yes, the initial bleaching out of algae from green to gray is due to destruction of chlorophyll, but chlorine continues to oxidize many other organics in algae.


So if you are proposing not to use chlorine to control algae growth, then what do you propose should be used instead?  When CYA is in the water, then an FC level sufficient to prevent algae growth isn't particularly high in active chlorine (hypochlorous acid) level -- technically less than that found with an FC of 0.1 ppm and no CYA.  At this level, the 3-log kill times for most fecal bacteria are on the order of 1 minute.  Do you want the disinfection level to be slower than that and if so, by how much?


Phosphate removers do remove phosphates by precipitating them so that they can get caught in the filter.  If you have a lot of phosphates, then the lanthanum phosphate precipitate settles to the bottom of the pool and can be vacuumed or swept to get to the filter.  Assuming the filter is backwashed or cleaned, the phosphates are physically removed from the pool.  If there aren't a lot of phosphates, then the water clouds and eventually the particles get caught in the filter.


I notice that one of your products is using tetrachlorodecaoxide (TCDO) to produce chlorine dioxide in chlorinated pools.  I've been trying to get some manufacturers in the U.S. to consider using chlorine dioxide in pools as well, but no one has spent the $1-2 million it would take to get EPA approval (most of the cost is for safety/toxicity studies; the rest for efficacy via EPA DIS/TSS-12).  Chlorine dioxide is effective against Cyrptosporidium parvum and it does not produce as many disinfection by-products (THMs in particular) as chlorine.  However, in chlorinated water, chlorine dioxide can produce chlorate which is something the EPA regulates so that would need to be dealt with.  On your webpage I linked to on TCDO it says the following:


Where other forms of chlorine dioxide produce chlorites (note the ‘t’), TCDO and free chlorine do not. Instead, they produce chlorides (note the ‘d’ ).


Huh?  First of all, TCDO has the systematic (IUPAC) name of "molecular oxygen tetrachlorite hydrate", O2•4ClO2(-)•H2O, which makes it more obvious that the compound contains four chlorite and when dissolved in water results in chlorite ions.  These chlorite ions then react with chlorine to produce chlorine dioxide.  The undesirable by-product of chlorine reacting with chlorite is the creation of chlorate ion (so is that what you meant?).  However, keeping chlorine concentrations lower keeps chlorate production to a minimum.  In fact, there are water purification tablets that make chlorine dioxide by combining sodium chlorite with Dichlor such as Katadyn Micropur MP1 Purification Tablets (also described here).  Interesting that it's good enough to drink, but not approved for swimming.




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