Calcium deposits in heater

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glennx99

glennx99

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Bronze Supporter
Sep 25, 2016
19
Bloomington, IN
Hello-

We've had issues with calcium deposits forming in our heat exchanger causing reduced flow and the heat exchanger to overheat, eventually actually melting the plastic side panel on the heat exchanger. Manufacturer's reps suggested lowering the pH from 7.5 to 7.3 and felt that it was pH spikes causing the problem. We use Metal Magic for stain control. I found this article (if the link doesn't work Google "aqua magazine the case of the mysterious pool deposits"). It suggests that HEDP in the pool can result in unwanted calcium phosphate deposits in the heater. Has anyone else had this experience? Our pool heater runs off and on until the pump turns off and there is no pressure, potentially leaving still water in a hot heat exchanger.

Debating on what to do - drain the pool and move from Metal Magic to something like Sequa Sol? I've forwarded the link to our pool people plus to the manufacturer's rep to consider.
pH 7.5
CH 150
TA 100

Thanks for your help!
 
Calcium scale builds up due to improperly balanced water. Keeping your pool within TFP recommended guidelines will prevent scale. Pool School - Recommended Levels.

If you are unable to keep one or more levels in range then you will have to manage your CSI to compensate. PoolMath will give you the number after you enter all your test results. Keep CSI between -0.3 and 0 to prevent scale. Tweaking pH and TA is usually sufficient to move the CSI into range. More here, Pool School - Calcium Scaling
 
Given your low levels of CH, calcium phosphate scale is highly unlikely. However, the HEDP sequestrant you are using can interfere slightly with the CH test so your exact CH level is unclear.

Do you know what your phosphate levels are? The article you cite describes a calcium phosphate scaling problem because the acid they were using was a mixture of both hydrochloric and phosphoric acid. That led to exceedingly high PO4 levels as the phosphoric acid is a direct source of orthophosphates. HEDP has to oxidize and breakdown from chlorine exposure to form orthophosphates and that process is a lot slower.
 
I would suspect that low flow is the primary issue. Is there a bypass on the heater?

If the pool is kept hot, that can increase the risk of scaling and ph rise. Has the ph ever gotten really high?

In my opinion, allowing for heater cooldown is important. Some manufacturers say that it's not necessary but I think that it's always better.
 
If you knock off some of the "scale" and grind it up in a mortar and pestle you can test to see if its calcium scale or phosphate scale or both...

Eg, if you add MA and it fizzes a lot, its likely calcium. But if it doesn't, you can mix it with a bit of distilled water and use a cheap phosphate strip test - you're only testing for presence, not amount (which will be wrong.)

If the scale sample acts more like phosphate scale...then you can cobsider the whole testing and rdcing route.

But first see if cool down cycles help. Eg shut down heater at least 20 min before turning off pump.
 
Thanks for the suggestions. Our heat exchanger is shot and will be replaced later in the month. Here are some responses to the issues raised:
1. The heater comes on and off based on the pressure from the pump - I'm thinking that turning it on and off daily or installing a time switch for the heater might be a good idea so that the heater cools off before the pump shuts off.
2. We keep our pool pretty warm - 85.
3. Re phosphate levels in the water I have a Jack's Magic test kit for their sequestering agents - does that measure phosphates in the water? I also bought a test kit for aquariums - maybe read that somewhere here or online. It maxes out at 3.0 mg/L but I'm not sure how that translates into ppm.
4. I do have sample scale bits and can get some muriatic acid and see what happens. Can also do the test with distilled water - both good ideas.
5. I live in Bloomington, IN and have contacted the chemistry department to see if they will do some analysis for me in return for a gift to IU.
6. Regarding low flow I have read that it can cause scaling. A junior and a senior Hayward technician were here and did not bring that up.
7. My chemistry has been within normal limits for TFP but when I add liquid chlorine to the pool, or Borax to raise pH, the water clouds up.
Please feel free to respond to any or all of the above!
 
Which Jacks Magic product is it? If it's their HEDP based sequestrant then the kit measure phosphonates, not phosphates. The aquarium test kit is fine but you have to determine if it reports its concentration in units of phosphate [PO4] or in units of phosphorous [P].

1 mg/L = 1 ppm

Phosphates in pools are normally measured in parts per billion (ppb).
 
^After a whole lot of foolin around on this topic this spring, I am comfortable saying that the Aquarium kit measures PO4...I've learned that total phoshates can only be measured in lab after a lot of hijinks. The po4 is what you want to know.

You can also use distilled water to dilute your reading and read to a higher number.

At first, I ddnt believe hubby's aquarium kit reading via dilution...until i bought a $50 hi-limit Hanna instruments po4 meter and discovered the readings were in accord, allowing for dilution margin of error.

The aquarium kit undiluted will read to 3,000 ppb once you translate mg/l, which is 500 higher than the highest available pool pi4 test kit.

But if you have any desire to accurately read to 30,000 ppb the http://Hanna instruments Hi Limit tester is the next best thing to pricey pro gear. (sorry I couldn't link directly to the meter but their site sent working right on an old iPad)

Once you get a sense from the aquarium kit whether the scale is positive for phosphate and less reactive for calcium or not, post back. There's a lot more I can share on this topic but its eye-glazing and dependent on myriad variables, some of whch make my head hurt and involve a lot of math ;)
 
Again thanks for the suggestions. I did obtain muriatic acid, as one member suggested, and dropped some scale into it. Pretty much nothing happened, perhaps slight bubbling but almost imperceptible. I then took another piece of scale, added distilled water, and ground it with a mortar and pestle (granite). Using an aquarium test it maxxed out for phosphates. I then rinsed everything and tested distilled water sloshed around in the mortar and it tested no phosphates.

To clarify the Jack's Magic question - I have not been using a Jack's Magic product as a sequestrate, I have been using Proteam Metal Magic. I might be wrong on this but I believe it uses HEDP and the Jack's Magic sequest test reads very high.

Re pH this is an indoor covered (when not in use) pool that doesn't get used a whole lot. The water chemistry is very stable especially if using liquid chlorine instead of pucks. On possible culprit, and I'm to blame for this, is adding liquid chlorine through the skimmer when the pump is running. I will discontinue this practice.

We have a water lab here in Bloomington that will test my water for phosphates; for the scale I would need to send samples to Indianapolis (though a local chemistry professor may be able to help me with that).

Re flow: I texted the Hayward representative and told him that the issue of flow had come up both on this website and also from another source. He felt that it was not an issue with our heater. His response: "There is not much that can go wrong with the bypass on the manifold, and the spring system appeared to be in-tact"

This is a great forum! Thanks for everyone's input!
 
Glenn, the phenom of phosphate scaling in swg cells or heaters is not well known or researched in the pool industry to date. But the "math" that can predict its occurrence was shared with me last year by ChemGeek because on well, I'm a high toll Metal Magic/jacks user who went years with very little water change. Because I also use soft water and lower calcium levels, some techs, eg Jack's, theorized that my po4 level was so high because the sequestrant was not bonding with calcium and being carried out. It is known that phosphonic acid over time will break down into p04.

I'm posting a section that cites the equation leading to po4 scaling in the event you're interested.

I had a water change (trucked in) this year due to liner change, and replaced my 15 year old heater due to exchanger failure. I did have heavy scale that tested positive for po4, btw. (I should have saved that exchanger for science ;)

I've arrived at my own conclusions about all this, but take it with a grain of salt. In my case, I plan to do annual or semi annual po4 removals to avoid the 25,000-plus (actually, 50,000 last year) type of levels. But I continue to use a swg-specified product (jacks purple) because between swg and fill water, I don't feel anything else manages metals better and I do not appear able to remain metal free. But I plan to do my future po4 removal with pure Alum, the type you must floc and vac to waste, because in the correct conditions, it will also remove iron.

I have to get to a meeting, but here's the formula background:

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

So you can see that at the elevated pH in the SWCG cell that calcium phosphate formation can occur at rather low CH levels. So unless your CH is very low, you'll probably need to lower your phosphate levels in your pool. The least expensive way to do that (other than water replacement) is to use Orenda PR-10,000 where removing 25,000 ppb phosphate in 22,000 gallons will take somewhat more than 1.4 gallons. Of course, you don't need to remove all the phosphate but even removing half would take a lot of product. As shown in this link the product is $139 per gallon. If you add this very slowly to the skimmer (maybe even in split doses) you might avoid the cloudiness and not need to use a clarifier. Obviously do not backwash your filter for a while (say, a week) after adding the phosphate remover.
Click to expand...
 

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Am currently in NYC but have ordered phosphate testing things. Will also have our city lab do an analysis on the water to double check. I am seriously considering using a phosphate remover to bring levels down if they are high as I don't really want to drain the fiberglass pool any more than absolutely necessary. Will have more data next week.

the article in Aqua Magazine I referred to in my initial post suggests that calcium phosphate is driven out of solution by high temps (as when the pump shuts off while the heater is still running) rather than high pH (like calcium carbonate). Does this jibe with your experience? I should probably hav a timer installed on the heater....
 
Was anxious to get back to Bloomington to test the water for phosphates. Per a member's suggestion I got a Hanna high limit tester and it was waiting for me to get back . I ran the first test and maxed out the meter at 30 ppm. I redid the test diluting 1 unit of pool water with 3 units of distilled water. The meter read 11.3 which would translate to 45,000ppb. Wow. I heated up some pool water in a stainless steel sauce pan and didn't notice a whole lot happening until the water got really hot - close to boiling - at which point it started turning cloudy. Based on pH of 7.2, TA 100, CH 185, I would have expected to see more action at a lower temperature (using the formula posted above and elsewhere). But I imagine the formula only tells you when precipitation will *start* and the hotter you get the faster it goes. So now I'm debating on draining and refilling vs using phosphate remover.
 
SeaKlear Commercial PR removes 9,000ppb per 10,000 gal of pool water per quart of product. So assuming your pool is 20k gallons, you'd need 10 quarts of the product to reduce your PO4 levels. At ~$40/qt, your looking at $400 in chemicals.

How much to drain and refill the pool? Can you do it with metal free water?

Also, the equations posted are thermodynamic relations. They tell you IF scaling is likely, not how fast it will proceed.
 
Hi Glenn!
That reading is credible to me since my own exceeded that ;)

Last spring I'd attempted reduction by using the commercial Seakleer product but at the time hadn't resolved accurate testing. At the volumes you'd need to remove, the Seakleer will form like a floc. It will take several vacuum to waste efforts to remove, even though its designed at lower doses to be removed by filtration. My experience was not successful, though I can't explain why. One theory is that the phosphonic acid continues to break down daily into new po4. This is not to suggest that Seakleer isn't a suitable product for "regular level" removal...Matt and others have used it successfully.

For the price and hassle of using a product like this at high volumes, if I were to do it again, I would seriously first consider a water change, even if it were only a partial just to scale back the concentration to less problematic levels. I don't think a zero goal or even low goal is realistic for those on well water...

Or, what i plan to try next spring to control a minor build-up from this year, i will instead try Leslies Alum specifically, but would really pay attention to creating ideal ph levels (low) to use it. The reason I will be trying Leslies Alum, which is a true floc, is because it also reduces iron load as well as phosphates.

With that said, alum floc sometimes fails to form, especially it seems if ph is higher. But the comparative price for product ($25 ish) makes it less painful if it fails ;)

I've read a great deal on water treatment processes since my spring journey as water plants struggle with these same issues, it appears. Alum is typically the cost-effective method deployed.

Hope that helps give you a starting point.
 
So Glenn, there is a long, complicated deepend thread on a similar topic full of possible errors chronicling my removal attempts for new swg...I am going to link you to Matt's post therein about calculating volume of Alum needed, and note TreatmentNerd's 3:1 ratio from work (is in wastewater industry).

Here it is: Phosphates.....are they worth removing?? - Page 16

This little section starting there might assist you.
 
Thanks for posts. Some additional information to factor in
a. Bloomington city water is soft (despite all the limestone around here)
b. city water has very little dissolved metals
c. the city does NOT add phosphorus products to the water
d. the down pipe attached to the skimmer has a patch on it making the use of the vacuum problematic
e. when a pH change in the pool results in cloudiness the filter eventually, albeit slowly, is able to remove it
 
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