spa pH and total alkalinity: spa water chemistry - the spa pH and total alkalinity

The topics of pH and total alkalinity are inter-related and are key parameters (factors) in the overall pool water chemistry. pH is the relative acidity or alkalinity of the water. The pH scale goes from 0 (most acidic) to 14 (most alkaline) A pH of 7.0 is neutral. Ideally, spas and hot tubs should be maintained in the 7.2-7.8 range for a variety of considerations: sanitizer effectiveness, bather comfort, corrosion, cloudy water and scaling. Total alkalinity is a measurement of the total quantity of alkaline materials present in the water. Low TA allows for rapid pH fluctuations, makes pH control more difficult and can contribute to corrosion. High TA makes pH adjustment more difficult and can be a contributing factor in cloudy water and scaling. A TA range of 80-120 PPM is considered optimum. Control of the spa or hot tub water chemistry is necessary to assure optimum pool water quality. Clicking on the underlined and highlighted "keywords" or "catch phrases," in the archived answers will give you access to additional information on that topic or product. Please refer to the Glossary, if there are terms or phrases that require explanation.

It seems that the pH of my spa is always too high. After I switched from chlorine to bromine, it started to happen Can that have anything to do with the problem? The water is nice and clear, but the pH definitely seems to be very high. I keep adding a pH reducer, but nothing seems to be happening. I need some help.

The problem can very well be related to the bromine. However, the fault lies, not with the bromine, but with the chemicals used to test the pH. Bromine can react with phenol red (chemical used to test for pH) and cause a purplish-red color that makes it appear that the pH is very high. In fact, the formation of this color has nothing to do with the actual pH. The problem lies in the fact that the phenol red solution may not have had enough neutralizer (to prevent bromine from reacting with phenol red) in its formulation. This leads to false high pH readings. I assume that the bromine, that you are referring to, is a solid form of the product. In this case, you are using a bromine source that is acidic in nature and that should preclude the need for you to ever have to add acid reducers. Spas maintained, in this manner, will require pH increasers and total alkalinity increasers - never acids. I suggest that you bring in a water sample into a local spa professional for confirmation. If confirmed, you need to use a pH Test Kit that is formulated to work with Bromine or add a drop of chlorine neutralizer (available in most pool and spa stores) to the test vial, just prior to adding the phenol red solution. Now that we have established why the pH can actually be very low, we must take another step. The low pH could have caused corrosion of the heater. In order to avoid discoloration or staining, I suggest that you add a double or triple dose of a Quality Spa Mineral Treatment, prior to raising the pH and total alkalinity. I hope that I have been helpful. Good luck and enjoy the spa.

What a great web page! Maybe you can help us. We have a new spa, to which we added PERFECT PH at start up. We had the water tested yesterday: pH 7.0, Alkalinity 220 ppm, Hardness 20 ppm. Unfortunately, no one seems to be able to help us. High Alkalinity according to the maker of the Liquid pH Buffer is normal and should be ignored. However, bringing the pH up now is proving difficult. Is this a drain the tub and start again situation? We are concerned that high alkalinity. may cause problems, on the flip side, also low pH. Hardness we can fix with calcium chloride, I assume? Thank you so much for your help!

Matthew & Julie C., 6/5/2004

There is no compelling reason to maintain the TA in the 80-120 PPM, so long as the water is clear, there are no signs of scaling and the pH is in range. In your case, the pH is too low. The pH Buffering product that you added will make it harder to raise the pH. The good news is that once the pH has been adjusted, it will tend to remain there for longer periods of time. Your hardness is curiously low, as most testers have difficulty measuring a very low reading. The pH Buffering product should not be used in hard water areas. If you increase the hardness, you may cause the water to become cloudy. Normally low hardness brings the issue of corrosiveness. However, in you case, the high TA and a correct pH should reduce this possibility. However, there are other benefits to consider, such as reduced foaming, at higher levels of calcium hardness. If you choose to raise the hardness, I suggest that you keep it at approximately 150-200 PPM. Under no circumstances go over 250 PPM. To better assure proper overall spa water chemistry, visit a pool/spa store that has a very reliable, professional lab such as a WaterLink or Pinpoint system, rather than a less accurate test kit or strip reader. To locate a dealer near you, go to: www.lamotte.com/pages/pool/expdeal/index.html I hope that I have answered all the questions. Enjoy the spa.

My pH is good and the spa water looks great, but my TA is too high. Every time I try and lower the TA to below 120 PPM, the pH ends up too low. Raising the pH ends up raising the TA. It is like a roller coaster ride!. Any help would be appreciated.

It is more important to maintain a proper pH, than it is to maintain a TA of 80-120 PPM. Minerals that occur naturally, in your water, might be contributing to this phenomenon. There is no compelling reason for you to have to lower the TA: your pH is good and the water is clear. Stop worrying about the TA, unless there are signs of cloudiness, the appearance of calcium scale or other water chemistry problems. Work on maintaining a proper pH!!! Leave the worrying to those with very low TA, that are unable to keep the pH from bouncing. Enjoy the spa experience.

Hi Alan, first off....great website that seems to be helpful without an agenda. My question has to do with high T/A and pH. I have high T/A of just under 400 and pH of around 8. This is after adding a half cup of baking soda to the water as I thought T/A would be low and pH low due to some faulty pH test strips. I would like to add some muriatic acid to bring all in line, but don't know how much for a 450 US gal tub. Also would like to know how long I should wait after adding that baking soda and also should I keep the circ pump going or full jets when adding? Thank you in advance.

First of all, you do not have to add any baking soda. That is for raising the TA and it is already too high. You need to add acid. Usually the pH reducing chemical for spas is sodium bisulfate. It is just easier and more pleasant to use. The end result is the same, with either one. It will lower the pH and the TA. Just use the filter on recirculate. Add the sodium bisulfate (pH Reducer), 4 ounces at a time, until the pH is 7.2-7.6. At that point stop! If the TA is too high, there is no need to do anything, so long as the water is clear and there is no sign of scaling. If by chance, the TA is too low, add some baking soda (TA Increaser). Remember, you can always add more - you can't take out. Not all test strips are the same. I suggest that you try the LaMotte Insta-Test product, as I have not received any negative feedback. For more information, go to www.lamotte.com I hope that this information proves helpful.

I have a commercial spa that is being controlled by an auto controller. We are using liquid chlorine as a sanitizer and carbon dioxide as a pH controller. Our source water has a pH of 7.2, TA of 95 and CH of 120. The operator finds that the TA tends to creep up after a few days and she is forced to lower it with acid. Is there a correlation between either the sodium chloride or the carbon dioxide and this creeping affect? If so can you recommend a solution to this situation. Note this tub is completely drain every four to five days based on it current bather load. Regards.

Liquid chlorine has a high pH and you are being forced to lower the pH. Your choice of carbon dioxide will be effective, at lowering the pH. The byproduct of the carbon dioxide gas and the alkaline materials in the liquid chlorine are bicarbonates. This forms the basis of total alkalinity. So long as the pH is correct, I would not be concerned with the TA, if the water remains clear and there is no sign of scaling. With the relatively low calcium hardness, a higher TA will actually make the water less corrosive. Otherwise, keep the pH closer to 7.2 and the TA will become lower. pH is always the more important parameter. I hope this information helps resolve the matter.

Dear Alan, your website is great. Have learnt a lot but have not found my answer. We have got a new spa and although we have followed the instructions on how to fill a new pool our pH and TA is totally out. The pH is over 8 and the TA over 220. What chemicals should be added when filling the spa? Ours is a 1,000 litre spa and we use chlorine. Thank you in advance.

Adding pH reducing chemical will drop both the pH and TA. I suggest you add 120 grams (4 oz.), at a time, every 15 minutes, until the pH is 7.2-7.6. It will probably take several additions. You can always add more chemicals -- you can't take out! Once the pH is in range, test the TA. If the TA is over 120 PPM, there is no compelling reason for you to have to lower it further, so long as the water is clear, there are no signs of scaling and the pH is 7.2-7.6. If the TA is under 80 PPM, add some TA booster, about 120 grams (4 oz.), until the level rises above 80 PPM. pH is always more important than total alkalinity. I hope that this information helps get you off on the right track. Enjoy the spa.

I test my pool and spa chemicals daily as I work for a hotel. My problem is I have to adjust the pH in the spa quite often. All the other chemicals tend to stay within range. So far all the pH adjustments have been to raise the pH and the amounts of soda ash I add have all been guesswork. What I need to know is if there is a formula to determine the proper amount of chemical to add for proper pH adjustment. I have been to your website and think it is great. I hope you can help me with this. Sincerely.

There's no simple, foolproof formula. The amount of chemical required to raise the pH is dependent upon the water volume, total alkalinity, additions of acidic chemicals such as bromine tablets, the absorption of carbon dioxide and the bather usage and frequency. No two spas would be alike. Apparently, you are using a sanitizer or system that lowers the pH. It is more or less inevitable that the pH will drop. I suggest that you keep a log, as a means of better determining the corrective treatment for your spa. I hope that I have been of help.

What household substance can be used to increase or decrease total alkalinity in my hot tub?

David W., 5/30/2005

None to lower the TA! Sodium bisulfate (pH reducer) is normally used to lower the pH and/or the total alkalinity. It is not a household chemical and is a strongly acidic chemical, in a granular form. Muriatic acid could be used, but given the small volume of water in a spa, it is too strong to handle easily and conveniently. Acidic materials like vinegar are too weak and should not be used. Baking soda (sodium bicarbonate) is the chemical used to raise the total alkalinity of spa water. I hope that this information proves useful.

► Constant High pH?

The pH seems to be in the high 8 all the time and total alkalinity seems to be low around 50 at least that’s how many drops it takes to turn red from green. My tub is 1000 gal, temp 104, calcium hypochlorite is the chlorine and reads 5 PPM free chlorine. The water is clear all the time I do get lots of foam as well. Got any ideas?

Leonard B., 11/14/2006

Calcium hypochlorite is a poor choice as a sanitizer, in your situation. It has a very high pH and will cause the pH to remain high, if adjustments are not made. High pH makes chlorine less effective and makes formation of foam causing soaps more likely. Try adding a spa formula antifoam. Adding a periodic dose of an enzyme can help destroy the body oils that lead to the formation of soaps. The addition of an ozonator is something that you might consider, as it will make maintenance easier and produce higher quality water. It will reduce the chemical consumption. You might add a mineral sanitizer, as well. The combination of the two work well together. All you should need is a very low level of chlorine or bromine, as it will act as confirmation that proper conditions are being maintained. To further assure optimum water quality and to reduce chemical usage, you might add a MicroPure high efficiency spa filter cartridge. Your water testing might be improved and simplified by using LaMotte Insta-Test strips. I hope that this information will prove helpful.

Sincerely, Alan Schuster, 11/15/2006

► Corrosion Problems?

I had been treating my hot tub regularly, however all of a sudden the water became very corrosive and the handle used to pull yourself up and out of the tub corroded and the rust fell down into the water. Now I have the rust ring all around the water line, the filter has turned brown, and the handle is corroded through with many pin holes in it. I drained the tub and the stains are extremely hard to remove. Also can the handle be replaced, so it doesn’t continue to cause problems? Where did I go wrong and how can I rectify the situation to get my tub back useable? Thank you for your assistance.

Larry Weigle, 1/27/2008

Acidic conditions will lead to corrosion of metal parts and, possibly, the heater. It sounds like the pH was too low! Try using ascorbic acid (vitamin C) in a sock and scrub the stains. Refill and add a dose of metal treatment. I suspect you were using bromine tablets and neglecting to monitor the pH. The addition of an ozonator is something that you would be wise to consider, as it will make maintenance easier and produce higher quality water. It will reduce the chemical consumption. You might add a mineral sanitizer, as well, since it will provide additional, persistent sanitizing. The combination of the two work well together. All you should need is a lower level of chlorine or bromine, as it will act as confirmation that proper conditions are being maintained. To further assure optimum water quality and to reduce chemical usage, you might add a MicroPure high efficiency spa filter cartridge. Replace the handle with plastic or stainless steel. Keep the pH at 7.2-7.8, the TA at about 120 PPM and the calcium hardness at about 200 PPM. I hope that I have been helpful.

Sincerely. Alan Schuster, 1/28/2008

I have adjusted the total alkalinity of the spa to about 100 and the pH is good. Still within a week or so, the pH is too low. The only chemicals I use are bromine tablets in a floater. The spa has an Ozonator and is only used a few times a week. What can I do?

Spa water does have a natural tendency to drop in pH. What you are describing seems to be quite normal. The absorption of carbon dioxide and the effects of bathers tend to lower the pH. The bromine in your floater will lower the pH. All this results in a slowly falling pH. If your TA wasn't 100 PPM, it would happen much more quickly. I suggest that you test the pH, at least every other day and adjust, as required. Enjoy the spa.

My total alkalinity readings are around 50 PPM and the pH of the water is 6.9. How should I treat the spa water? Thanks in advance.

In all likelihood, adjusting the total alkalinity (TA) will also raise the pH and bring it into the ideal range. Use a Spa Formula Total Alkalinity Product and follow the directions. It is important to avoid low TA, as this can lead to low pH readings and pH fluctuations. The combination of low pH and TA, in your spa, can lead to corrosive conditions and could damage underwater metal surfaces and the spa heater. Testing the water on a regular basis is important! I hope that I have been of help.

The low TA may contribute to the corrosiveness of the water and how it effects metal parts. You might want to adjust the controller to maintain the pH closer to 7.6. The addition of sodium bicarbonate will raise the TA, with only a slight raising of the pH. One-half a pound should raise the TA approximately 50 PPM. Bathers, wastes and aeration tend to lower the pH and the TA over time, making the adjustment of the TA somewhat dependent upon usage. If your spa water has a calcium hardness below 300 PPM, you might be able to add a pH buffering product. These are liquid products, based upon potassium phosphate, and will help stabilize the pH and the TA, in the ideal range. However, it is not suitable for use in hard water situations, as it will lead to cloudy water. I hope that this information proves helpful.

Thank you for helping me. I have a Spa Frog Mineral Sanitizer (silver ion?), and an ozone generator that runs 24 hours/day. When I filled the spa about 10 days ago I added sodium bicarbonate to bring TA up to 80 - 120, sodium bisulfate to bring pH back to 7.4, and lithium hypochlorite. Since then I only add sodium bisulfate and dichlor as needed to maintain pH and free chlorine. Testing with both spa test strips and a swimming pool (OTO/phenol red/TA titration) test kit give the same results. The spa is covered 23+ hours per day. I did add a small amount of defoamer once and a small amount of clarifier once, but the pH problem existed both before and after those chemicals.

The defoamer and the clarifier have no appreciable effect on the pH. Ozone is pH neutral and the Spa Frog mineral sanitizer, that you are using, should have no significant effect on the pH. Dichlor is essentially neutral. The lithium shock has a very high pH. It appears that you are using relatively soft water, inasmuch as you had to raise the total alkalinity. I suggest that you keep the pH at 7.2-7.6. If the pH is too low, add sodium bicarbonate to raise the pH. This will also raise the TA. The higher TA will help stabilize the pH more effectively. A higher TA is not a problem, so long as the calcium hardness is not over 200 PPM and the water remains clear. Dissolved carbon dioxide is acidic. As you add sodium bisulfate, you are converting some of the dissolved carbonates and bicarbonates into carbon dioxide. As this gasses off, the pH will drop. Maintaining a higher TA should solve the problem. The OTO test kit does not measure Free Chlorine, as can the Test Strips. I hope that I have been helpful.

The last time I picked up spa chemicals I noticed a liquid product that is used to buffer the pH and make it more stable. The product advised against being used in hard water areas. I believe that my water is soft. Should I be concerned about using the product.

This type of product can cause precipitation and cloudiness if used in hard water areas. These products should not be used if the Calcium Hardness is above 300 PPM. Even at levels between 200-300 PPM, precipitation and clarity problems can result, depending upon the pH and the total alkalinity. Personally, I suggest that such a product, not be used, if the calcium hardness of the spa water is above 200 PPM. You should be able to adequately stabilize the pH by maintaining a total alkalinity of 80-120 PPM. However, these pH Buffer Products can work very well in soft water areas and can reduce the frequency of pH adjustments. I hope that I have been helpful.

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