Spa Calcium Hardness and Scale

How to manage calcium hardness levels in spas, swim spas and hot tubs? Calcium is a naturally occurring mineral that is frequently found in high concentrations: such water is called "hard" water. Calcium hardness is one of the important spa and hot tub water chemistry parameters and its control is important to help assure proper water quality. Calcium problems do not normally impart a color to the spa water, as does the presence of metals such as iron and copper. The preferred range for spas and hot tubs is 80-200 PPM. Low levels of calcium can lead to possible corrosive water conditions. Chemicals are available to raise the calcium hardness, as might be necessary. High calcium hardness levels, especially above 400 PPM, can lead to possible water clarity problems and scaling conditions. Various chelating or sequestering Mineral Treatment Products are available to help deal with the problems associated with high calcium hardness levels. Spa or hot tub calcium hardness levels can be determined by a simple water analysis. This is especially important with well water, as other problematic minerals might be present and could require treatment. Spa Water Magnetizers, also known as Magnetic Water Conditioners have been reported to help reduce and eliminate scale formation, by inducing a positive electrical charge in the water passing through the return lines. If problems arise, refer to the Spa Problems Page, as a source of problem-solving information, broken down into various categories.  Scroll down the page and click on the linked keywords, catch phrases or images, in the archived answers below, to access additional information, on that topic or product.

Do you know what's in your water?  If you're having problems, with hard or soft water, testing allows you to better understand the chemistry and determine the cause of the problem.  Once understood, you can select the best treatment option, such as the addition of a Magnetic Water Conditioner.  Understanding the nature of the problem, should be step one.  For information about our full selection of testing options, visit our Test Equipment Store.

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► Using Softened Water In A Spa?

I am planning to purchase a hot tub in the near future and would like to fill it with softened water. Does that present any special problems? The dealer seems to think that I shouldn't use softened water. Thanks for your help.

Brian R., Troy, NY, 11/13/2020

If your household water is of such poor quality, as to require a water softener, you are better off using softened water and avoiding the possibility of mineral problems. You can easily add chemicals to adjust the pH, calcium hardness and total alkalinity of the softened water and, by doing so, avoid any possible corrosion problems. The balancing of the pH, hardness and total alkalinity, of the softened water, should completely eliminate any objections from the hot tub manufacturer or the dealer. Water softeners do not always remove heavy metals, such as iron. If you use the METALTRAP Filter to treat all water added to the spa, you will avoid the possibility of metals causing staining and discoloration. A single METALTRAP can be used to refill a typical spa, 20 times or more.  If this website was helpful, in answering your question, please consider joining our E-Letter Mailing List.  I hope that this recommendation works out for you.

Sincerely. Alan Schuster, 11/14/2020


► Starting Soft - Ending Cloudy?

Hi, Alan. Thank you for this question service. I have SPA and live in high alkaline area. Our water is from a small private water company. The TA is 240. Total hardness of about 250. I start with soft water and add CaCO3 to raise hardness. Our well water starts out at 400 total hardness. I'm in the pH TA YoYo.  I'm using sodium bi-sulfate and sodium carbonate. I am using a lot of Potassium Peroxymonosulfate to control the cloudy water. Is there something to raise pH without raising TA? What would you recommend? Thanks.

Greg C., 10/10/2018

I agree that you are better off using softened water, under your circumstances. If you are really using calcium carbonate (CaCO3) you're using the wrong chemical. You should be using calcium chloride (CaCl2)! Calcium carbonate is not soluble and is probably responsible for the cloudy water. Calcium chloride is water spa dealers should be offering to raise the hardness level. I suggest that you empty and clean out the spa. Refill and enough calcium chloride product to boost the level to about 200 PPM. Add enough TA booster, sodium bicarbonate, to boost the TA to about 100. At this point, you should have an acceptable pH. If not add a small amount of pH Increaser. In the future, you should not require pH Reducer. Raising the pH will always raise the TA, which is why you try and keep the parameters within a range and not at a specific number. Good luck and I hope that I have been helpful.

Sincerely. Alan Schuster, 10/11/2019


► Gritty Spa Surfaces?

I have had my spa (400 gallons) for over a year now. I changed the water for the third time two weeks ago. I adjusted the water (pH, Hardness, Alkalinity, etc) and did not go in it until last night. The entire bottom and sides of the spa had a sandy, gritty residue. It was like sitting on sandpaper. I cannot determine what has caused this or how to remove. The water is crystal clear and I can see no real color to the grit. I scrubbed the bottom and with the jets running, the gritty residue just returned within minutes. Please help!

Ken R., 12/3/2012

What you are describing could be due to high calcium hardness, combined with high pH and/or TA. The gritty deposits are, in all likelihood, calcium carbonate. Adding a calcium hardness treatment and controlling the pH and TA, should improve the situation. If you enter the test results into the formula found on the Langelier Index Page, it will help determine the scaling tendencies of the spa water. To better assure proper overall spa water chemistry, visit a pool/spa store that has a very reliable, professional lab such as a WaterLink SpinTouch Lab or Pinpoint system, rather than a less accurate test kit or strip reader.  I hope that this information will help solve the problem.

Sincerely. Alan Schuster, 12/3/2012


► Low Spa Water Calcium Hardness?

The water in my area is soft. Do I have to adjust the hardness of the spa water? Thank you.

Pawtucket, RI, 10/3/2012

If you make sure that the pH and total alkalinity are always optimum, the soft water may not be a big problem. However, soft water can add to the corrosiveness of the water and this can lead to damage of underwater metal surfaces. In addition, the soft water will support higher levels of foaming. Foam must, at least occasionally, be totally eliminated for good spa water sanitizing. To raise the calcium hardness, test for calcium hardness and use a Spa Formula calcium hardness increaser, as directed. This is not an expensive proposition and is worth doing, especially, if the water is very soft. I hope that I have been helpful. Enjoy the spa.

Sincerely. Alan Schuster, 10/3/2012


► Suffering With Scale?

We live in a hard water area. I've had problems with my spa due to scale forming. Besides the scale deposits, I've had white flakes shooting out of the returns. Any suggestions?

J. H., Mesa, AZ, 5/6/2018

You could fill you spa with soft water, that is if you have one. Some manufacturers recommend against using soften water, but if you adjust all of the spa water chemistry parameters - especially the calcium hardness, pH and total alkalinity - to within normal suggested ranges, there should be no problems. You could add a calcium sequestering agent and try to keep the pH closer to 7.2 and the TA, if possible, within 80-120 PPM. A spa water magnetizer or magnetic water conditioner is another possibility. This strap-on device has been reported to help reduce spa calcium scaling problems, as well as improve some other spa water parameters. There are models to treat pools or an entire house.  I hope that I have given you some options. Good luck.

Sincerely. Alan Schuster, 5/6/2018

► Questionable Hardness Level?

We are having a hard time getting are levels balanced we  have only had the spa for a couple of weeks now and are at a loss! Our dealer hasn't been much help.  We are using a 6 way strip that is telling us the level of hardness is at 1000 ppm or greater. We have a softener that we used to fill the spa and still it is high. Is there any way of bringing this down and what damage can this cause?  We are using a starter kit and we are also trying to bring down the pH (8.4) and Alkalinity (180). I have dosed the tub 3 times with 3 TBS of the pH down and still it is high. The tub is 357 gallons.  Also the strips say that the stabilizer is Ok at 50. What is this? Is this the sanitation level?  If not how do I check the sanitation? Sorry for all the problems. We feel like idiots and I actually did well in chemistry.  Hope you can help make sense for us! Thanks.

Heather, 9/28/2006

If you filled the spa with softened water and I would have advised you to that, it should not be 1000 PPM. If you use softened water, you should have added enough calcium hardness to raise the hardness level to 200 PPM. I suggest that you have a dealer confirm this reading and make sure that your softener is working properly. High calcium hardness can lead to scaling problems and cloudy water problems. Adding a regular dose of a scale treatment or a Magnetic Water Conditioner can help. When the calcium hardness is high, it becomes even more important to maintain a proper pH and a total alkalinity close to 100 PPM. High TA and hardness are going to make it more likely that you will have to add more pH down, than might have been suggested on the product label. Keep adding it until the pH drops into the 7.2-7.6 range. That will lower the TA, as well. The stabilizer is not really relevant, if the spa is covered most of the time, which is almost always the case. Assuming that you are using chlorine, the proper level for adequate sanitation is 1-3 PPM of free chlorine. In the interest of providing better sanitation, with less effort and chemical usage, you might consider adding an ozonator and a Mineral Sanitizer. It will make for better bathing conditions. I hope that I have been helpful. Enjoy the spa.

Sincerely. Alan Schuster/ 9/29/2006


► Spa Heater Scaling?

I've had problems with calcium flakes in the bottom of my hot tub and have already replaced the heating element because of severe calcium buildup. The pH, alkalinity and bromine levels are always within normal parameters. The calcium level is consistently low and dealer says I should be adding calcium which I have been doing. What I don't understand is why I should be adding calcium when I have what seems to be too much calcium. I've already had one repair and am concerned about causing further damage. The dealer seems to be as mystified as me.

Bruce F., Toronto, Canada, 4/29/2005

This doesn't add up! Any spa that has exhibited problems with calcium scaling should not be adding calcium hardness booster. Even if it was added, it is not something that is added more than once, unless water was removed. It is either not calcium hardness that caused the problem, the chemical added was not calcium hardness booster, the pH and TA fluctuated wildly or there was a testing error. I suggest that you start at the beginning. Have both the spa and tap water tested for calcium hardness. Even better might be total hardness. To verify the test results, have another local dealer test similar samples. If you truly have maintained the pH at 7.2-7.6 and the total alkalinity at 80-120 PPM, there is absolutely no need to have a calcium hardness level above 200 PPM. NONE! Sometimes, in the interest of keeping the pH more stable, pH Buffer products are added. There products should not be used when the calcium hardness is 200 PPM or more, as they can cause precipitation and cloudy water. Without the specific test results it is difficult to pinpoint the source of the problem. Feel free to get back to me with the test results and as much other relevant information as possible. I hope that I have been of some assistance.

Sincerely. Alan Schuster, 4/29/2005

► Adding Calcium: Liquid Or Granular?

What is the difference between using Liquid Calcium or Granular Calcium? Does Liquid calcium cause cloudy water when you put more than a few ounces in at a time? Granular does and you have to make sure you rinse the filters when the full dosage has been added. Any opinion on this? Anxiously awaiting your answer. Sincerely.

Denise G., 10/31/2007

Either way it is the same chemical and the same problems can happen. The liquid product is simply calcium chlorine dissolved in water. It is a convenience item and is easier to measure, when used in a spa.  I suggest keeping the level at 150 -250 PPM. High pH and/or TA can add to cloudiness problems. I hope this information is helpful.

Sincerely. Alan Schuster, 10/31/2007


► Adding Epsom Salts?

I just purchased a small used spa. I was wondering if I can use Epsom salts in the spa with the chlorine chemicals and also if adding a few drops of essential oils will hurt the spa or it's components in any way. Thank you.

Susan B., Prescott, AZ, 5/30/2009

Epsom salt are magnesium sulfate. Magnesium is a component of total hardness. Your water is already hard enough (Arizona), possibly even too hard. Adding magnesium sulfate will only increase the hardness and could, possibly, lead to scale formation and cloudy water. So the answer is no! Fragrance items are used in spas. However, these products are specifically formulated to be used in a chlorine environment. Essential oils can react with chlorine and form undesirable byproducts or do absolutely no harm. There's no way for me to be sure. I would not suggest that you add any essential oils to the spa, unless specially labeled, as being formulated for use in spas.. I am sorry that it might not be want you wanted to hear, but it is better to be safe than sorry. Enjoy the spa.

Sincerely. Alan Schuster, 5/31/2009


► White Stuff?

I have found what looks like white flakes on the spa floor. This has happened a few times. Any ideas about the source? Thank you.

Kelly N., Scottsdale, AZ, 12/13/2009

The likelihood is that the white material is calcium scale that has flaked off the heater or underwater plumbing, due to the turbulent water action. Judging from your Arizona location, it is a good bet that your water is quite high in calcium hardness. In order to avoid calcium scale deposits, that could lead to a loss of heater efficiency and water clarity, try keeping the pH closer to 7.2 and the total alkalinity in the 80-120 PPM range. These steps can help reduce the scaling tendencies of the water. The addition of a quality Spa Mineral Treatment, on a monthly basis or upon the addition of makeup water, will help avoid or reduce scale formation. The addition of a Magnetic Water Conditioner can help control the problems caused by high calcium hardness and is simple to install. I hope that I have been of assistance.

Sincerely. Alan Schuster, 12/13/2009


► Sandpaper Texture?

A few weeks ago I replenished the bromine tablets in our spa. For some reason they had gotten crushed, but I went ahead and used the powder. Two days later when we got in the spa, all of the underwater surfaces had a sandpaper texture. I tried draining the tub half-way and adding fresh water to see if the "stuff" would redissolve, but it didn't work.  We know we will need to drain the spa, but how do we get the stuff off without damaging the surface? It is adhered to every surface. We use well water that we know is very hard. Thank you.

Carol R., Eagle Point, OR, 3/26/2008

This has nothing to do with the tablets and everything to do with the high calcium hardness. If using softened water is an option, I would do it. You can always add chemicals to make the softened water right for spa use.  You can use acidic cleaner or scale removers to clean the surface. If you drop the pH to about 6.0, the scale will come off easier. However, make sure that there is no bromine present or copper corrosion can occur in the heater. Three factors contribute to scaling conditions: high calcium hardness (usually over 400 PPM), high pH (usually over 7.8) and total alkalinity (usually over 200 PPM).   All three together make it even worse. You can lower the pH and TA with acid. The calcium hardness might be controlled, but not necessarily lowered, by adding a calcium sequestering agent. I suggest that you test the water for pH, TA and calcium hardness. The Langelier Index will tell you if the water is scale forming and provide insight to help improve the situation. A Magnetic Water Conditioner can help control the problems caused by high calcium hardness and is simple to install. I hope that this information proves helpful.

Sincerely. Alan Schuster, 3/25/2008


► Feels Like Sandpaper?

I have a film on the inside of my spa that feels like sandpaper. It comes off with a scrubby pad. What is the problem? Thank you.

Sue, 8/17/2010

It sounds like calcium scale: a deposit of calcium carbonate on the underwater surfaces. The cause is high levels of calcium hardness, usually over 400 PPM, coupled with high pH and/or total alkalinity. A spa water analysis will confirm this possibility. A simple way to help deal with this problem is by adding a Magnetic Water Conditioner. Refer to the page on Langelier or Saturation Index for some more information on dealing with this problem. You should adjust the water chemistry as possible and add some scale treatments. I hope that this information will prove helpful.

Sincerely. Alan Schuster, 8/18/2010


► Soft Water Foaming?

We have a new 500 gal spa. Our new home has very soft water (hardness 85) and this seams to be a problem. I have kept a handle on the chemicals (bromine) but seams that after 3 week of very little use (2hrs) the water is clear but when the jets are turned on the water turns white and foams. I noticed that after I used an algaecide it began to do this but I only added very little. I add calcium to boost the hardness level and wonder if it needs other minerals. I have contacted several places but no one has the answer or if the lack of chemicals in the water is the problem. It has become a pain....almost ready to sell it. HELP

Nancy H., 8/8/2016

Spa water that is soft is more likely to foam. Raise the hardness to about 200 PPM, by adding a calcium hardness booster. Antifoam can be used to help control the foaming. Algaecides are not normally used in spas. If the product you added contains dimethyl benzyl ammonium chloride or something close, it should not be added again. This type of algaecide will cause foaming, even in a pool. An aerated spa makes it much worse. With proper sanitation, there is no need to add an algaecide. I hope that this information will prove helpful.

Sincerely. Alan Schuster, 8/8/2016

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