Phosphate scaling

Swampwoman

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Apr 27, 2012
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Grand Rapids, MI
EDIT: This was separated from the thred "Phosphates: Are They Worth Removing?" in the deep end.

For continuity and background on high phosphate levels on gas heaters for well users and the methods of phosphate removal dscussed in this branch, please see this link, from about page 16 onward:
Phosphates.....are they worth removing?? - Page 22 )

***

Lol. But I'm not allowed to use the chainsaw anymore after what happened last time I tried to cut up a tree ;)

Here's my rough outline of experiment at removing 25,000 ppb - shared for future well users or folks like Glen from Bloomfield who had po4 scaling in his heater last year:

1. Based on chem calcs back on pg 16, I think I will need about 20 lbs Aluminum Sulphate to remove much/most of the PO4 in my 24k gallon pool - vac to waste, not communicating with filter.

2. Then I will treat monthly with the Seakleer commercial Lanathum chloride, which is better in smaller doses (and much more expensive but runs through filter at smaller doses.)

Matt, I don't know where to find this out so if you know, please share:

1. Would the Alum also floc salt? CYA? CH? Eg. What all does the charge combine with, beyond phosphates, crypto, etc. (not that I have crypto...but this is a treatment for it...)

2. I do not have a heater bypass. Is this a known problem in any way? Yes, the ph will be lower during the treatment, eg. About 24 hours until I rebalance. The alum itself will drop the ph a bit...plus is most effective just under 7 according to what I've read.

The heater guy and I discussed a bypass loop in depth but I just don't have room to do it right and he shares that opinion. We'd decided if heater went down in winter I'd do an emergency bypass with flex if I has to wait a day or so for service (he'll be in the Keys ;)

3. I won't be running the swg, but is there any risk of combined particles sticking to the plates? I have a dummy I could plumb, but I'd rather not if I didn't have to.

Thanks in advance.
 

JoyfulNoise

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So, to answer your questions -

Salt & CYA will not be affected by the floc. Calcium could potentially be affected by floc but only if there was calcium scale in the water as particulates. So I wouldn't expect any of those parameters to change much at all.

A bypass loop isn't needed for something as transient as a floc process. Just turn off the heater and it will be fine.

SWG should be fine too. Just turn it off.

Let us know how it goes.
 

JoyfulNoise

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Just realize that using 20lbs of aluminum sulphate floc will result in about 28ppm sulfate ion concentration in your water. Sulfates are definitely bad for SWGs although 28ppm shouldn't present too much of a risk. If a pool owner were to regularly floc their SWG pool, then switching to polyaluminum chloride (PAC) floc would be preferable.
 

Swampwoman

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Thanks!
Re:
using 20lbs of aluminum sulphate floc will result in about 28ppm sulfate ion concentration in your water.
I believe back on page 16 of the other thread, you and/or TreatmentNerd had suggested that keeping it under 75 ppm was ideal, right? But if sulphates don't "go away" then I'd want to avoid alum next time, depending of how much water turns over in a year from backwash and carry out.

If I don't have to bypass, I was thinking about doing it this weekend...but it looks like temps may be back up in the 80s...so I might wait another week. That will still give me two weeks to get sorted before the dome goes up ;)
 

Swampwoman

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Three quick things with more to follow after Alum Floc Phosphate Removal Experiment is complete.

1. Pentair has just this week come out with a titanium heat exchanger...interesting as Matt joked about. Me needing same ;)

2. Was running ph lower, eg 7.2 ish in prep for scheduled floc tonight..and no scale the last 2 nights since its been lower. Intriguing.

3. PO4 read 26,800 tonight prior to floc...up 1680 ppb from Sept 2nd reading. Now we know approximate rate of decay. Eg 500/week approximately.

Pics of process....I'm just gonna say it kinda hurts to take that beautiful, clear water from pic 1 to pic 2 ;)

But i have clear evidence i need to develop a strategy to prevent phosphate scale buildup on heater. Fingers crossed that after vac-to-waste sessions when I read PO4 this weekend I will have made a dent.

Applied 20 lbs Alum pre-dissolved in bucket (two batches), based on calcs from my bucket test last year.
-Floc is forming - am running circ only for 2 hours and had backwashed filter prior.
-Water is 90 degrees.
-After reading more per WQ articles specific to Alum as po4 remover, I adjusted ph down to 7 and have soda wash ready for tomorrow should the alum drop it further. That move was because efficacy increases to 93-95% removal rate if ph is between 6.5 and 7.
-Found a source n Amazon for technical grad alum fr not much more than $1/per pound...so used 15 lbs of that plus the 5 lb bucet from Leslie's. if it works, this is waaaaaay cheaper than lanathum chloride.

With my blue light in my pool now looks like curaçao ;)

image.jpgimage.jpgimage.jpgimage.jpgimage.jpgimage.jpgimage.jpgimage.jpg
 

JoyfulNoise

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Hey, the Pool Store would say those pictures after floc look just fine!! You can see the light....


Hehehehe....interested in your results tomorrow [emoji848]
 

Swampwoman

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5 am pics (have a long day today)

Turned circ off at 10:15 pm. At 5 am, floc forming reasonably well...in my previous bucket test, it formed and dropped best at ph of 6.9, which was as low as I tried it. Hopeful that by the time I get home tonight its fully dropped ;)

image.jpgimage.jpgimage.jpg
 

Swampwoman

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Day time pics of floc formed...got much of it out tonight but have to re-fill to finish and have another 7 am meeting ;) no po4 testing until I've gotten it all out and run filter a bit and backwashed, so I'm thinking Sunday for results.

image.jpgimage.jpgimage.jpg
 

Swampwoman

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Hmm...will have to try to figure out how to get it as there's not much left, only deep end/side crevices out of reach. Maybe I'll see if I can get someone to catch some off the waste line when I do my next vac during lunch.
 

needsajet

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If you have some small pipe or conduit around, maybe 1/2" and a couple feet longer than your depth, you could dip it in the pool down to the precipitate, then suck like a straw, cap with your thumb, and lift it out... maybe :)
 

Swampwoman

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Lol. Decided sipping alum probs not good for my health, but we did attempt to catch some from waste line.

After second vac yesterday, I adjusted ph back up and started up the pump/filter. Here's a night shot for comparison. That's a and of light n te middle, not floc.
Gonna wait til its light out and try a po4 read.

image.jpg
 

Swampwoman

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Ok, not sure what to make of these test results, but we'll call it progress, if highly imperfect ;):

PO4 read immediately prior to treatment Wed night: 26,800 ppb

PO4 read this am after 2 vac to waste sessions, ph adjustment, and 20 hours of filtering: 10,900 ppb

Total removal of PO4= 15,900 ppb

Sorta control = wastewater collected from waste line during vac (mix of floc and water) : 28,400 ppb

SO - $20 worth/20 lbs alum (aka 9060 grams) in 24,000 gal (90,849 litres) of water removed roughly 60% of 26,800 ppb po4

BUT: called 2 sequestrant mfgs and got 2 answers re whether or not the Alum would also remove my active polyphosphate (HEDP). One said yes for sure with conviction. The other said no ;)

Water Quality documents imply "yes" in that they use Alum to reduce all organic and inorganic phosphates.

Iron read this am with Hanna meter in treated water is 0.0. Iron read in wastewater was .06. Iron read from source prior to filling was .33.

This leads me to believe I still have active sequestrate in water...or trace Alum in filter is pulling it out. I guess time will tell.

So, not sure what to make of that...where did the source water iron go? If flocced, I'd have expected higher wastewater read, but if complexed with phosphate, maybe not. Curiouser and curiouser as they say.

By comparison, commercial Seakleer is rated to remove 9,000 ppb per 32 oz in 10,000 gallons. In my experiment last year with 2 gallons I did not achieve anywhere near that rate but initially didnt have the more accurate testing and was therefore diluting with distilled water to the order of 10. So those results were NOT especially valid.

If Seakleer normally works as rated, I'd expect to have needed 135.68 ounces to have removed 15,900 ppb from 24,000 gallons (eg more than a gallon at between $119-$139 plus shipping) so the Alum is without question more cost effective.

I just wish I had a better handle on removal rates and conditions. My in-treatment ph was 6.5 after te impact of the alum and i don't think I'd be comfortable going lower but that is within the ideal phosphate removal range.

In water plants, they also agitate it vigorously and I wonder if for my purposes 2 hours on circulate was enough.

I think I need to revew molar weights - not my strong suit ;)

With repect to avoiding phosphate scale on the heater, I may need to do a second treatment. I will test to see whether or not smaller doses of lanathum chloride through filter impact pressure with higher po4. If not, I can treat weekly...the issue is that backwashing in winter/dome is a bit problematic. Had I gotten to zero, I could have just waited to retreat in spring.

If my accumulation rate is about 2500/mo, this treatment bought be six months of reduction. Not bad at all considering the challenge, but not quite what I'd hoped ;)
 

JoyfulNoise

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Sounds like the alum was successful for you in reducing phosphates and metals. I agree that alum floc is a lot cheaper than the lanthanum chloride phosphate reducer but there are drawbacks -

1. Needs vacuum to waste;
2. Needs water replacement (see #1);
3. Needs chemical adjustment (pH) prior to use;
4. Adds sulfates;

#4 can be eliminated by using polyaluminum chloride floc. #1 & #2 (???) are deal breakers for me.

As for the possible removal of HEDP, I suppose it depends. At pool water pH a large fraction of the HEDP will be ionized with a negative charge. The HEDP could interact with the aluminum cations and gelatinous aluminum hydroxide and be pulled out of solution. The only way to know for sure would be to get a Taylor phosphonate test kit.

Speaking of phosphonate testing, perhaps you should consider getting a test kit? You use a lot of sequestrant and you might benefit by knowing the exact levels that work for your pool and how quickly they are oxidized by your SWG. This way you can dose more effectively and perhaps reduce your consumption rate. It’s a lot like chlorine testing - you could just dump a gallon of bleach in your pool everyday and not bother with testing thereby letting the FC swing all over the place or you can test & dose properly and thereby use less chlorine overall.
 

Swampwoman

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Yes, Number 4 is the only deal breaker for me because at my volumes of PO4, seakleer's lanthanum chloride DID floc in my pool and it was actually a bit harder to capture and vac to waste ( by one or two extra sessions.) That's partly because it didn't drop quite as nicely/uniformally.

I was thinking about getting a sequest test if only to determine what's in the water now.
 

JoyfulNoise

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Just so we’re clear, the lanthanum chloride phosphate remover for most NORMAL pools is supposed to be filtered out, not vacuumed to waste. And we know your PO4 levels are decidedly NOT normal [emoji6]
 

Swampwoman

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^Yes, posterity note: floccing via Seakleer is only a phenom at a gallon or two in a single application ;) Applying their chitosan clarifier will assist in getting remnants.

So, in other news, I suspect Jack's sequest test is based on the Palin drop test for boilers (based on the color conversion.) If it is, both Palin and Taylor test kits for polyphosphonates are interfered with by po4, iron, flouride, etc. because each test is actually measuring coverted po4.

My high po4 levels might exceed the capability of performing the blank.

I'm wondering if I wouldn't be better off figuring out the rate of acid I need and boiling a sample to convert te HEDP to po4, and then using the colorimetric kit and reagents I already have in the Hanna test kit to test both the "blank" (at 10,900) and then the "boiled."

I would not need or want to add an oxidizer because I don't want total/organic phosphates, I want to isolate the polyphosphates, right?

Matt, do you have any suggestions for a kitchen version/DIY of this?

I would buy one of the other drop kits, either Jacks or Palin or Taylor, but their range is lower, and I'd be buying more molybdenum when I already have it.

The Hanna kit is based on the heteropolyphosphonate molybdenum blue method from the WQ standard 18.
 

JoyfulNoise

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I don't believe the Taylor test is a colorimetric comparison; unfortunately, I can't get to the Taylor website to check. You are correct that most other tests use an oxidation process to convert organic phosphonates into inorganic phosphates and then a second step to measure the phosphate level generated. That is why a blank correction is necessary in order to measure the background level of inorganic phosphates first so you can subtract it out.

The Taylor test, last time I looked, is an actual titration test and it measures phosphonates in their typical range of application (maintenance level ~ 8-15ppm with a high range of 30-50ppm). The test is sensitive to a wide array of phosphonates (ATMP, HEDP, etc) and so the conversion factor in ppm/drop depends on the species you expect to have (in your case, it's all HEDP).

Again, when the Taylor website comes back online (it's offline for me, some weird server error on their end), I can look and see what the interferences are but I don't remember if background phosphate levels matter at all since the indicator dye may only be sensitive to phosphonates. Of course, a quick phone call to their tech support line should clear up any lingering questions.