Phosphates 1000, to worry or not to worry?

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J

jamesk9

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LifeTime Supporter
Sep 16, 2011
8
Mount Belvieu, TX (20 miles east of Houston)
I know in the pool school, it said phosphates are irrelevant as long as you keep your FC in check... except in extreme circumstances. Was just making sure this wasn't an extreme circumstance. I know some of my figures are off target, but this was the first check of the season.


20,000 IG with diamondbrite finish

FAC 4
TAC 4
Salt 3200
CH 200
CYA 50
TA 190
Ph 7.8
Acid demand 4
Copper 0
Iron 0
Pho 1,000
Temp 68

Thanks
 
Welcome to TFP!

Your FC is at the bottom of the range for a CYA of 50. Your goal range is: 4 to 8 ppm.

Your TA is high - you will want to lower that to help with your pH drifting up...But right now with that water temp your CSI is 0.13 which is great. Lowering your pH to 7.6 will put you at -.06 which is also great. Use Pool School to run different scenarios and see what happens when you modify TA, etc.

Since you went to Pool School you already know this, but I thought I'd repost it for convenience:

FC 3-5 ppm
PH 7.5-7.8
TA 60-80
CH 50-300 for vinyl, 220-320 for fiberglass 250-350 for plaster
CYA 70-80
Salt 200-400 ppm ABOVE recommended optimum level
Borates 30-50 ppm (optional)
 
I too just had my water tested by Leslie's since my CH re-agents seemed to have gone bad and were reporting 0 calcium. I was shocked to see that Leslie's uses the same Taylor test reagents that we use! No "machine analysis" like some of the others I've been to. I got the same report of 1000 for phosphates (highest he'd even seen) and the same line about using 2 liters of phosfree then weekly treatments after that. His claim was that high phosphates will cause greater chlorine consumption if not kept in check. I have never been concerned about nor tested for phosphates before.

Other than the desire to sell yet another pool chemical, why is the pool store concerned about phosphates but the consensus here is to not worry about them? From a chemistry perspective what role do they play in the overall makeup of the water? If FC drops too low and you have high phosphates should you then be concerned? Why?
 
The full answer is somewhat involved. Algae requires phosphate to grow. If there isn't any phosphate in the water, then no algae can grow. You can still have other (serious) problems, but you won't get algae. Phosphate comes in several forms. Phosphate remover only removes the most common forms. So it is possible to have phosphate in the water and not be able to remove it with phosphate remover. But by and large, phosphate remover can remove enough phosphate that algae can't grow.

Your average pool owner doesn't pay much attention to their pool. They consistently allow FC to get too low and then shock the pool regularly to try and recover from the problems that occurred because FC was too low. Sometimes, when FC didn't get too low for too long, a simple "dump this in and then ignore the pool" approach to recovering from the too low FC level works. But if FC is too low for too long algae gets going and recovering from low FC becomes challenging.

If you use enough phosphate remover consistently enough you probably won't have algae. You might spend a lot of money (which pool stores like) and you might have cloudy water (phosphate remover often clouds up the water for hours to weeks), but you won't have any algae. Thus, recovering from periods of too low FC becomes much simpler. The "dump this in and then ignore the pool" approach to recovering from the too low FC level always works.

The approach we promote involves never letting FC get too low. As long as you never let FC get too low, you never have algae, or excess chlorine consumption, regardless of your phosphate level. Since you need to add chlorine anyway, the minor level of additional attention required to keep the FC level high enough is usually fairly simple and certainly inexpensive. It is certainly less expensive than paying for phosphate remover, which can get pricy, and less aggravation, since you never get cloudy water.

However, there are lots of people in the world who don't want to pay that kind of attention, don't want to know how their pool works, and simply dump stuff in according to the schedule suggested by the pool store. For them, spending lots of money on phosphate remover can improve their experience of the pool, no more algae even when FC goes to zero, so no more problems getting rid of algae.

The excess chlorine consumption comment has to do with another issue common to the not paying attention pool owner. If you use trichlor, the CYA level gets really high, and this kind of person does not increase the FC level to compensate for high CYA. That means their FC level is too low, often way way too low. There is a strange thing that can happen when CYA is high and FC is low, but not zero. Algae can often grow, but grow slowly and nearly invisibly. There is enough chlorine to keep the algae from ever getting out of hand, but not enough chlorine to ever kill all of the algae. When this happens, your chlorine consumption goes up significantly. You actually have algae, but you can't see it, so you don't know what is happening, the only obvious symptom is that chlorine consumption went up. If that is happening, phosphate remover can often get rid of the algae, and thus stop the excess chlorine consumption. Of course shocking the pool will take care of it as well, and you won't get into that situation in the first place if your CYA level was reasonable.

Another twist: in some areas, including where I live, the water company actually adds significant amounts of phosphate to the tap water. If you live in such an area, using phosphate remover can get wildly expensive and very very annoying. Topping off the pool is constantly adding phosphate, and removing phosphate is expensive and tends to cloud the water. So your phosphate level goes back and forth and the pool store tells you that you aren't using enough phosphate remover. Sometimes this can get very dramatic, with the water remaining perpetually cloudy as you never manage to remove all the phosphates and constantly add more phosphate remover. Of course there are other places where the tap water phosphate level is very very low and the airborne phosphate level is also very low and using phosphate remover is very easy and not especially expensive.

And one more challenge: occasionally there can be enough phosphate in the water for algae to grow but in a form that the phosphate remover can't remove. That isn't all that common, but when it does happen phosphate remover is completely useless.

Overall, I would much rather pay just a little more attention to my pool. maintain an appropriate FC level, and not bother spending any money or time on phosphate remover.
 
Thanks for the detailed break down Jason. Is there ever a level where the scale tips based on the amount of phosphate in the pool? For example, would the recommended FC level ever be consistently higher just because there is more phosphate than what is considered normal? Or should keeping the water balanced based on normal recommendations keep the phosphate in check no matter what its concentration is?
 

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Removing phosphates from pool water to stop algae is like trying to remove the contents of a house to prevent break-in theft. Technically, it works, but it's cumbersome and comes at a high price. And people can still break in, they just can't steal anything.

One other thing about letting chlorine levels drop to "I-have-algae-and-must-use-phosphate-remover-to-fix-it" levels... There is not only no chlorine to kill the algae, but there is no chlorine to sanitize the water. Phosphate remover may thwart the algae growth, but it won't make your water safe.
 
3des said:
Is there ever a level where the scale tips based on the amount of phosphate in the pool? For example, would the recommended FC level ever be consistently higher just because there is more phosphate than what is considered normal? Or should keeping the water balanced based on normal recommendations keep the phosphate in check no matter what its concentration is?
Click to expand...
The short answer is no. Phosphate is not the only limiting factor to algae growth. Ultimately, the rate of growth is also limited by sunlight and temperature, both of which have optimum levels which allow for maximum rates of growth for particular species of algae. Giving the algae more phosphates than they need for that rate of growth does nothing. Even under ideal conditions, algae only double in population every 3-8 hours, depending on species.

Now, that said, a pool rich in algae nutrients (phosphates and nitrates) with warm water and ideal amounts of sunlight can be very "reactive" in that letting the FC get too low for too long has the algae grow seemingly quickly, but as noted with the growth rates it really isn't that fast. It's just that with the FC too low for an extended period of time or near zero for a day, then with 3 hour generation time algae can increase in number by a factor of 256 in 24 hours. Usually it takes a couple of days before this becomes noticeable, either as increased chlorine demand or as cloudy water. Of course, keeping the appropriate FC/CYA ratio keeps the chlorine killing algae faster than it can reproduce. The Chlorine / CYA Chart is designed to prevent algae growth regardless of nutrient level for most algae (green, black) and other organisms and pathogens (white water mold, bacteria, viruses, protozoa except for Cryptosporidium parvum oocysts) except for yellow/mustard algae which needs to be eliminated explicitly (or a higher maintenance FC/CYA level is needed, but most people choose to completely eliminate the algae instead).

Note also that the organic phosphates that the phosphate removers do not remove are only slowly taken up by algae, but are rapidly taken up by bacteria and converted to the inorganic phosphate that algae can use more rapidly. If the FC level gets close to zero such that bacteria can grow, then you can rapidly convert one phosphate form into another so you can go from a situation of apparent control to one that seems out of control fairly quickly and likewise phosphate tests can go from apparently low phosphate levels to high ones.

As Jason notes, it is just so much simpler to not worry about phosphates and instead maintain the appropriate FC/CYA level. In any event, phosphate removers should be seen in the same vein as algicides -- something that isn't necessary, but is a supplement you can use at extra cost if for some reason you are not able or willing to maintain the appropriate FC/CYA level. If one wants a supplement (which again, isn't really necessary), we normally recommend using Polyquat 60 weekly since it has fewer side effects or one can use 50 ppm Borates since they are also a mild algicide.
 
Also, note that phosphates are reported in parts per billion, whereas most other chemicals are reported in parts per million. 1,000 ppb is only 1 ppm. Therefore, the number looks much more serious than it really is.
 
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