How Much Baking Soda to Raise Alkalinity in Hot Tub

Recently we were asked the question how much baking soda was needed to raise alkalinity in a hot tub.

The question was a bit vague as we needed to know the existing pH reading and also the volume of water in the hot tub to give a proper answer.

It seems the hot tub was dosed with chlorine to keep the bugs down – much like shock treatment, before a week of being unused during a vacation.

At the same time, the cover was set in place to keep the water clean and free from debris and upon the owner’s return, he checked the pH level and was surprised it was low – the water was acidic – his reading was 6.7 parts per million.

He wanted to know whether he had done any damage by leaving acidic water in his hot tub for a week, or whether it would do any long-term damage if it was left like that?

LEISURE TIME 22339-02 Up for Spas and Hot Tubs (2 Pack), 2 lb By the time he’d contacted us, he’d been trying to raise the pH level with Leisure Time’s SPA UP, following the instructions on the tub and had virtually neutralized the pH level, but the doubt was there and he needed answers.

There were a few issues…

Shock treatment using chlorine produces a more acid environment (the pH level drops) which in turn kills off most bacteria within a hot tub.

What normally happens when you shock a hot tub is within around two or three hours of the motor constant running and the top open to the atmosphere, the bulk of that surplus chlorine will have evaporated off to leave an almost neutral level which is basically what you are looking for.

By using the hot tub, we help the pH level rise a little further to a safer, more natural and comfortable place for our bodies, at the 7.2 – 7.8 reading, by shedding skin and other natural body microbes and bacteria.

His reading of 6.7 was due to the chlorine not evaporating off as the lid was left on to keep the water clean, and whether he left the pump running while he was away, he never said, but I feel that he perhaps didn’t.

So, more than likely he dosed the hot tub and covered it immediately before he walked away without evaporating off the surplus chlorine.

It’s so easy looking back on it in retrospect.

Bestway 54155E Hawaii Air Jet Inflatable Outdoor Spa

Leisure Time suggests using two tablespoons for every 500 gallons of water in your hot tub or spa when your initial reading is between neutral and 6.8 or 4 tablespoons when it is below that reading.

After dosing, let the pump keep circulating the water for three hours and then check the pH balance again.

To us, 3 hours is a bit of a long time for the small capacity of a hot tub – a small swimming pool, maybe, now that’s a bit more like it.

A good hour should be plenty with a hot tub capacity of around 250/300 gallons.


How much Baking Soda to Raise pH in Spa


But getting back to how much baking soda is needed to raise alkalinity in hot tubs; using everyday household items that you may already have in stock rather than having to wait days for a factory-produced chemical to be delivered, adds more stress and doubt in your mind about corrosion…

If you have shocked your water and it remains acidic, it needs to be neutralized by adding an alkaline-based product that will be dissolved in the water easily.


Et voila, BAKING SODA – what could be easier?

Baking Soda (1 Gallon Bucket) by Pure Organic Ingredients, Highest Purity, Aluminum Free, Food & USP Grade, For Cooking, Baking, Cleaning, & More! It is just a matter of sprinkling an ounce of baking soda into the water of a 250/300 gallon hot tub and let it dissolve naturally – twenty minutes should be plenty, then switch on your pump for an hour before checking the pH level again.

If it is still acidic, simply repeat until it gives the right pH reading!

Shouldn’t take more than a few hours to complete, then jump in and enjoy!!!


As far as corrosion of your hot tub goes

One week at that acid level will barely do any damage.

There are two options that may be affected here.

If you imagine a kettle acting as your hot tub heater, there are three common sorts of body:

  • Stainless steel
  • Plastic/acrylic
  • Aluminum

Each has an element inside to provide heating.

The least expensive hot tubs and spas tend to use the lighter ones, being the plastic or aluminum, with most of them plumping for cheaper plastic varieties as plastic is not affected in any way by acid or alkaline water and corrosion doesn’t happen!

On the other hand, aluminum will oxidize very quickly in an acidic environment and produce a form of aluminum that easily erodes into your water.

A sure sign of this is when your water starts to go a cloudy grayish color over a period of time.

It is barely discernible initially but becomes more cloudy as time passes as the filters do not trap this soluble aluminum. When it concentrates in the tub it gives this cloudy appearance.


Regarding the time-scale of erosion, one week isn’t such a problem, but if left for more than a month, then you are looking at the beginnings of replacement parts being needed and you would be lucky if your hot tub survived more than six months without major refurbishment.


With more up-market inflatable hot tubs, along with hard-sided portable hot tubs shown on another page of ours, a stainless casing is generally used which is unaffected by dilute acid. The remainder of the internals will be fine and the body/liner of your hot tub will be as original as it is impervious to acids.


So, put your mind at rest. A week with like that is no problem for your hot tub as manufacturers tend to overbuild their products to provide reliability for their customers and allow for simple water balancing mistakes that happen to most of us.

One good side effect for them – it reduces their ear-ache considerably.


Hot Tub Serum Total Maintenance Hot Tub Conditioner and Clarifier- 24 Weekly Doses


The best bet is to set up a weekly routine using Hot Tub SERUM to prevent many unwanted troubles developing.


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