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Heavy Calcium buildup/efflorescence above waterline. Struggling to get rid of it


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Hey!

It has taken way too long, but I finally realized that the white stains in my spa is most likely calcium buildup. The retailer of the spa told me it was because of the chlorine, but they honestly seem incompetent.. and any google searches resulted in people complaining about biofilm. I just discovered this forum the other day, and saw other people had the same problem here.

The buildup is very smooth to the touch, so not sandpaper/gritty like it usually is in most peoples cases. We've tried vinegar, baking soda, and scrubbing with pure calcium stabilizer on it. The stabilizer had the best effect but it's still extremely resistant. It seems like I need some heavy duty acid that wont damage the acrylic surface, so do any of you know anything stronger than the usual stuff?

I attached some pictures showing how it looks. The chlorine dispenser is the best reference as is shows how thick it is around pretty much the whole surface for about 2 inches above the waterline. The surface under the waterline shows no signs of calcium. perfectly smooth and no discoloring/stains. My theory is that with the lid/cover on, the steaming water attaches to the side of the tub before running down back into the water and depositing the calcium on the way.

If anyone has any great tips on how to get rid of it, Id be happy to hear. Thanks!

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My 2 cents:

 

22 hours ago, Leander999 said:

The chlorine dispenser is the best reference as is shows how thick it is around pretty much the whole surface for about 2 inches above the waterline. The surface under the waterline shows no signs of calcium. perfectly smooth and no discoloring/stains.

A few red flags for me here that might be related. You have a floater for chlorine in a spa? The only form of chlorine used in a floater is trichlor, which is very acidic and dissolves quickly at spa temperatures and can lead to high chlorine situations that can damage and oxidize plastic parts above the waterline in a covered spa. Trichlor is slow dissolving at pool temperatures making it useful in a floater but it's solubility increases with temperature making it an unsound choice for a spa. Calcium only precipitates out in alkaline conditions and only below and at the waterline, not above. It also is only on plastic parts from what I can tell in the picture. This would lead me to believe that is it not scaling but damage from low pH on the plastic. I can't see any on the acrylic shell so I don't know if it is present there also. High FC levels can also cause oxidation of plastic parts and what I see on your skimmer looks like this might be what is happening. I don't see a buildup. I see what looks like a degradation of the plastic surface. You stated that you keep your spa covered so their might be a buildup of chlorine gas or volatile oxidation byproducts under the cover causing this. Also, you did not say whether you have ozone or not. There should be NO residual ozone in the water but the way many manufactures install ozone there is and it can build up in a covered spa and cause oxidation damage above the waterline too.

 

22 hours ago, Leander999 said:

We've tried vinegar, baking soda, and scrubbing with pure calcium stabilizer on it. The stabilizer had the best effect but it's still extremely resistant.

Vinegar is too weak to have an effect on calcium carbonate. A stronger acid is needed. Baking soda is just an abrasive if used as a moistened paste and can damage the surfaces. Baking soda will also raise TA and that could increase scaling. (High TA and high CH is a recipe for scale formation and, in case you didn't know, baking soda is sodium bicarbonate is sodium hydrogen carbonate is alkalinity increaser from your dealer. They are all one and the same!) DON'T try using a Magic Eraser or other melamine foam sponge. They are very fine abrasives (like very fine sandpaper) and WILL dull and scratch the surfaces.

22 hours ago, Leander999 said:

and scrubbing with pure calcium stabilizer on it. The stabilizer had the best effect but it's still extremely resistant.

What is calcium stabilizer? Never heard of such a product. Please post the ingredients. IF the ingredients include any mention of the word calcium then it's a calcium hardness increaser. IF the ingredients mention phosphonic aicd, phosphonate, EDTA or Ethylenediaminetetraacetic acid (not a complete list but these are the most common ones) then your product is a metal sequetrant. Calcium is a metal. These will not lower the level of calcium in the water but will make it chemically inactive so it will not deposit as scale. They need to be added weekly. Over time (many months to years) they can have some effect on removing existing calcium staining and are the only way to remove calcium silicate staining  on fiberglass, acrylic, vinyl and other plastic surfaces. On plaster pool and spa surfaces a pumice stone is used to remove calcium silicate and an acid wash for calcium carbonate (or a pumice stone for waterline buildup on tile surfaces.

Now, under the assumption that the white stain is actually calcium (jury is still out on this, IMHO):

The only chlorine that will cause scaling is cal hypo (calcium hypochlorite) which adds 7 ppm calcium for every 10 ppm of FC added. Scaling occurs under conditions of high calcium hardness and high pH (which is normally linked to high total alkalinity) IF you are using trichor in your spa stop and switch to different form of chlorine other than cal hypo or switch to bromine if you want to continue using a floater. Trichlor requires a high TA to prevent pH crashes because it is so acidic. IT can also damage plastic parts because of it's low pH.

First question is how high IS your calcium hardness in the tub (strips won't tell you, they test total hardness only and magnesium does not cause hard scale.

Second question how high is the calcium hardness in your fill water,

Third question, Where is your pH NORMALLY and what is your TA?

Smooth white to grey scaling is often calcium silicate and not calcium carbonate and it's next to impossible to remove. The way to tell the difference is to put a few drops of muriatic acid on the scale. If it bubbles it's calcium carbonate, if it doesn't it's most likely calcium silicate. As I said above, the only way to remove calcium silicate from plastic, acrylic, vinyl, and fiberglass surfaces is by weekly use of a metal sequestrant (preferably one with a high affinity for chelating calcium vs. other metals like iron or copper, often sold as calcium hardness reducer) over a long period of time and only partial removal might occur.

 

 

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@RDspaguy @waterbear

Thanks a lot for the insightful information! You've clearly got some great understanding of how water and the chemicals work, which is nice to see when Im so lost and it seems like I got a one-off problem no one can give me concrete answers for..

First of all, you are correct. We are using a floater dispenser for tri chlorine as it was included in the "Chlorine chemicals starter pack" from the spa dealer. Something else noteworthy, is that it doesnt include any sort of shock treatment which Ive found strange as it seems to be the core of sanitizing. 

At first my theory was exactly as you say, that the chlorine gases stuck under the lid bleaches the parts, but I dropped the theory as the stains doesnt cover the entire surface above the water. It's a very distinct fade from the waterline up. As you say, Its very hard to notice in the picture which is why we didn't stress it too much at first. We got the spa just before winter time, only used it for soaks in the dark of night and didn't notice the stains around the edge of the acrylic. It's very noticeable when theres no water in it, but not too much filled up thankfully. I could get some closer pictures for you tomorrow if you'd like. 

The stabilizer description says it binds metal-ions in the water preventing calcium and other minerals from building up from hard water. 

I've only got the test strips as that is what the retailers supplied us with, and they claim pretty confidently that it is enough. Obviously this doesnt seem to be the case, and we should probably acquire some more advanced testing tech. If youve got any suggestions, Id be happy to hear! On the strips, the hardness in the new water is actually extremely low/soft after metal-gone and we're slowly building it up microdosing with the "hardness up" from the startkit, trying desperately not to start a second wave of calcium buildup from the new water.. The Ph is in the upper 7's as I took the advice from @RDspaguy and the alkalnity is also a bit on the high side, but if I understand correctly, you use Ph down to adjust the alkalinity as well, so I didnt mess with it to prevent getting a too low Ph.

Funnily enough, the SO managed to order Bromine by a mistake when we were resupplying, and looking up the differences and ability to swap, we decided to try it instead of chlorine this time (with new water, and a full clean of the tub)

The spa does have ozone, but I have not seen anything in the water that could indicate pollution (if its even visible). Probably worth mentioning is that the water has always looked pristine. Very clear and normal chlorine smell levels, and has been comfortable to soak in every time.

All the products we've tried to clean the calcium off with has been on the skimmer cover which is detachable and outside of the spa to not cover the shell or water with anything that could mess with chemical levels or cause soap/foam. I'll definitely get some muriatic acid to try this week. Other than that Im afraid I cant answer your other questions as Ive only got my test strips.. Ph and TA has been within the normal levels on the strips all of the time we've had the spa otherwise.(Ph between 7.2-7.8 and alk between 80-120ppm)

Many thanks again for the in depths answers. Its very appreciated!

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15 hours ago, Leander999 said:

At first my theory was exactly as you say, that the chlorine gases stuck under the lid bleaches the parts, but I dropped the theory as the stains doesnt cover the entire surface above the water. It's a very distinct fade from the waterline up.

This reinforces my theory of oxidative damage from the chlorine. It is usually not uniform and the fact that you are using trichlor in hot water also reinforces it.

It's a metal sequestrant, most likely phosphonate based. Calcium is a metal, which many don't realize. IF you have high calcium in the water then it will chelate it but has to be applied weekly since chlorine destroys it. It does not remove the calcium from the water.

15 hours ago, Leander999 said:

we should probably acquire some more advanced testing tech. If you've got any suggestions, Id be happy to hear!

If you are located in the US or Canada then you want a Taylor K-2006 test kit (not a Taylor K-2005). If you are in Norway (which your IP address seems to indicate unless you are using a VPN) try to find a test kit that uses liquid reagents and includes tests for Free Chlorine, Combined Chlorine (or Total Chlorine so combined chlorine can be calculated), pH (preferably with acid and base demand tests also because they can help make pH adjustments easier but they are not a requirement) Total Alkalinity, Calcium Hardness and Cyanuric Acid (chlorine stabilizer). These are the basic and necessary tests for a chlorine spa.

You also need to stop using trichlor and will need to add chlorine manually. IF you want the convenience of a floater then you need to switch to bromine.

https://www.poolspaforum.com/forum/index.php?/topic/53410-how-to-use-bromine-3-step-method/

 

15 hours ago, Leander999 said:

On the strips, the hardness in the new water is actually extremely low/soft after metal-gone

First, strips do not test calcium hardness, they test total hardness. Calcium hardness produces scale, magnesium hardness does not. Strips are useless for this test. You want a test for calcium hardness, not total hardness.

Second, the hardness is still in the water. It's been temporarily "chemically deactivated' but unless you are redosing the  sequestrant it can cause staining or scale, depending on the metals present in the water.

A more relevant test would be one of your fill water before dosing with metal sequestrant or your "calcium stabilizer" (which is basically the same as your "metal-gone" product) to see how hard the water actually is.

15 hours ago, Leander999 said:

The Ph is in the upper 7's

tell us nothing. We need an actual number such as 7.6 or 7.8 etc. Strips are useless for pH because they don't have the resolution needed (and the pH test in strips is notorious for being wrong anyway. Strips are precise (results are repeatable on the same sample) but just not accurate (producing results that are correct). In other words, the results are pure fantasy.

 

15 hours ago, Leander999 said:

but if I understand correctly, you use Ph down to adjust the alkalinity as well,

The act of adding acid lowers BOTH pH and TA at the same time. Here are some posts that explain a few things about pH and TA

https://www.poolspaforum.com/forum/index.php?/topic/52522-some-truths-about-ph-and-ta/

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

16 hours ago, Leander999 said:

alkalnity is also a bit on the high side

Once again, this tells us nothing. We need numbers.

16 hours ago, Leander999 said:

The spa does have ozone,

Once again, this supports my theory on oxidative damage.

16 hours ago, Leander999 said:

Very clear and normal chlorine smell levels, and has been comfortable to soak in every time.

use;less information, What are your actual Free Chlorine and Combined chlorine readings,and what is the Cyanuric acid reading? IF you are noticing a "chlorine smell" that usually indicates the presence of combined chlorine and that the water needs to be superchlorinated.

16 hours ago, Leander999 said:

Funnily enough, the SO managed to order Bromine by a mistake when we were resupplying, and looking up the differences and ability to swap, we decided to try it instead of chlorine this time (with new water, and a full clean of the tub)

Bromine is a different animal than chlorine. I recommend using the 3 step bromine method I outlined in one of the links I posted above. Also, you do not need to test for Cyanuric acid in a bromine tub and you only need to test for Total bromine. All other testing parameters are the same. The test kit that I recommend is a Taylor K2106 for bromine. If you get a kit that tests only for chlorine then you can test free chlorine and multiply the results by 2.25 to get a total bromine reading. Be aware that if youi are using a DPD test that it will bleach out and read low on both chlorine and bromine when sanitizer is above about 10 ppm leading you to think that the sanitizer is low or non existent when in reality is it very high, many strips have this problem also (including those based on syringaldazine instead of DPD . This is why I recommend the Taylor K-2006 and K-2106 since they both use FAS-DPD  testing which does not have this drawback if you are able to obtain them.

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