How Much Muriatic Acid to Lower the pH in a Hot Tub? – Learn How to Use Muriatic Acid in a Spa


how much muriatic acid to add in a hot tub to lower its ph

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At this website, I have already provided some tips about how you can lower the pH of your hot tub using acids.

In this process, one of the best acidic substance that you can use to reduce the pH of your hot tub water is a muriatic acid.

This specific chemical is strong, fast, and reliable to get your work done without any major issues if done with the right knowledge.

But wait, what do I mean by if done with the right knowledge?

By saying this, I mean that the process of lowering down the pH of your hot tub using muriatic acid will only work if you add the acid with the right quantity.

If not, your hot tub water may become more acidic and causes you severe skin rashes, skin burnouts, and other health hazards.


Because muriatic acid is a strong acid just like the hydrochloric acid that is used to clean bricks and concrete.

However, it contains a lower concentration of hydrogen chloride and that is what makes it a less dangerous acid.

But still, it is an acid and is highly corrosive and, if used inappropriately, can corrode anything from metal to plastic to your skin as well.

And after knowing all this, you definitely don’t want to experiment with this acid in your hot tub.

I have been using hot tubs for years and have come across numerous situations where I almost got my hands injured due to excess addition of muriatic acid to my tub to lower its pH.

Thankfully, now I have a proper idea about how to use the highly corrosive chemical properly to get my work done without any harm.

And today, I will be sharing this important information with you to avoid any unwanted accidents with you in future.

So now the question is, how much muriatic acid will you need to add to your tub to lower its pH safely?

Usually, you should add 12 oz of muriatic acid to every 10,000 gallons of water in your hot tub to lower the pH if it is around 7.6 to 7.8.

Similarly, if the starting pH level is in between 7.8 to 8 then add 16 oz of muriatic acid.

For pH of 8 to 8.4, add 24 oz (680 ml) of muriatic acid to your hot tub water.

And finally, for pH level of 8.4 and above, you need to add 1 quarter or 907 ml of muriatic acid to your 10000 gallon hot tub.

This simply means, if the pH of your hot tub is higher, then you will need to add more muriatic acid according to the actual level of pH.

This article is not over yet.

There are some important things about muriatic acid that you must know before using it for your hot tub.

So, make sure to read the article completely or else you might find yourself burning your own hands with the acid and causing skin issues later on.

Does Muriatic Acid Raise or Lower pH in a Hot Tub?

I hope you know the answer to this question.

As the name suggests, muriatic acid is an acid and due to its chemical properties, it actually lowers down the pH of hot tub water.

Being an acid, muriatic acid consists of a large number of hydrogen molecules.

And this high concentration of hydrogen molecules makes this chemical more acidic and thus corrosive in nature.

And we all know that the acids are on the left side of the pH scale and lie between 1 to 6 with the 1 pH chemical being the strongest acid.

The pH of muriatic acid is near or below 2.

From this, you may evaluate how strong muriatic acid is.

Being an acid, it will always lower down the pH of a higher pH liquid like water or bases.

Does Muriatic Acid Lower Alkalinity in a Hot Tub?

Yes, of course! When an element lowers down the pH of a hot tub, it can definitely lower the total alkalinity of the tub as well.

The exact number or amount to which the element will lower the alkalinity depends on different factors.

I will discuss about this topic in detail in another article.

As I mentioned in the previous section, muriatic acid has a pH of 2 which makes it a very strong acid.

And because it is a strong acid, it affects both the pH and the alkalinity of your hot tub greatly.

For example, where a certain amount of a moderate acid will lower the alkalinity of a 150 PPM liquid to 130 in 30 minutes, the same amount of muriatic acid can lower the alkalinity to 120 PPM in just 25 minutes.

Well, that was just for an example.

In reality, 20 Ounces of muriatic acid added to 10,000 gallons of water lowers its total alkalinity by 10 PPM.

Recommended Articles for You:

3 Steps to Increase Your Hot Tub’s Temperature up to 106 F

4 Methods to Reduce the Combined Chlorine Level of Your Hot Tub

2 Reasons that Cause Low Chlorine Level in Your Hot Tub

4 Steps to Follow to Switch from Chlorine to Bromine in a Hot Tub

How Much Muriatic Acid Needed for a 400-Gallon Hot Tub?

Not everyone can have a 10,000-gallon hot tub at his or her home.

I also did not have it in the beginning of my career, but later on as things progressed, I was able to afford my current 10,000-gallon hot tub.

So, how will you relate to this article then?

Worry not, let me make things simpler and more relatable.

In this section, I will be guiding you on how much muriatic acid you can use to lower down the pH of the water in your 400-gallon tub.

Yes, almost every moderate person can afford a small 400-gallon hot tub at home.

In the previous sections, we have learned that 12 OZs of muriatic is needed to lower the pH of a 10,000-gallon tub.

Now, using the same number, we will try to know how much muriatic acid is needed to lower the pH of a 400-gallon tub.

So, let’s do some simple math here.

For a 10,000-gallon hot tub, you need 12 OZ of muriatic acid.

Now for a hypothetical 1gallon tub, you will need 12  10,000 OZ of muriatic acid i.e 0.0012 Oz quantity.

So, you now know how much muriatic acid we need to lower the pH of a hypothetical 1gallon tub from 7.7 to balanced.

Now, just simply multiply 0.0012 by 400 to know how much of the acid you will need for the 400 gallon tub.

That equation comes about 0.0012  400 = 0.48 Oz

So, you will need 0.48 OZ (13.60 grams) of muriatic acid to lower the pH of a 400 gallon hot tub from 7.7 to balanced.

That was a fun calculation, isn’t it?

How Do I Bring the pH Level Down in My Hot Tub Naturally?

Let the chemicals be used in the laboratory only!

You don’t want to use chemicals to lower the pH of your hot tub water.

But you must do it to soak in your favorite hot tub again.

So, how will you do that?

Well, I have a solution.

One amazing and proven way for lowering down the pH of your hot tub naturally, without using any chemicals, is by using distilled white vinegar.

Yes, you can also use the vinegar which is available in your kitchen right now!

Vinegar is an easy-to-get item that you can easily find in your kitchen.

If not, you can also prepare synthetic vinegar in just no time as well.

To do that, just take 500 ml of water and 2 tablespoons of acetic acid.

Mix them up and hurray! Your synthetic vinegar is all ready to be used.

Coming back to the topic, how can you use it to lower your hot tub’s pH?

Just take four cups or 960 ml of white vinegar and pour it into the tub water after circulating the water in the tub properly.

After adding the vinegar, steer the tub water properly with a stirrer.

Also, make sure to keep the hot tub jets on so they can mix the water with the vinegar properly.

After that, wait for a few minutes and test the pH of the tub using a digital pH test kit.

If the pH comes down to 7.4 or 7.5, you are good to go.

So, this is a proven method that I personally use to lower my hot tub’s pH without using any kind of harmful chemicals.

I hope this works for you too.


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