Water chemistry in a hot tub can sometimes be confusing, one of the biggest misunderstandings is normally associated with TA or TOTAL ALKALINITY.
Here’s a detailed explanation by our water guru Andy.
WHAT IS TOTAL ALKALINITY?
Sodium bicarbonate (baking soda), TA PLUS is commonly used to raise both pH and total alkalinity.
Unlike pH—which is basically a scale to measure against—total alkalinity is a measurement of the concentration of all alkaline substances dissolved in the water. These substances are primarily carbonates, bicarbonates and hydroxides, along with a few others. These alkaline substances buffer pH in the water by neutralizing acids. In other words, total alkalinity is a measurement of the water’s ability to resist change in pH.
Total alkalinity is measured by its concentration in parts-per-million (ppm), and the ideal range is from 80-120ppm, depending on the type of chlorine you use. For example, Trichlor (STABILISED CHLORINE) has a low pH of about 3, which means you will want your total alkalinity closer to 120ppm, given how acidic it is. Calcium Hypochlorite (SHOCK CLORINE) however, has a high pH of 13, so you can have lower alkalinity, like 80-100ppm. Note ( DON’T USE SHOCK CHLORINE AS A REGULAR SANITISER)
Did you notice that total alkalinity is not measured on the pH scale?
This is an important distinction to make, because this is usually how pH and alkalinity get confused. Total alkalinity is measured by the amount (ppm) you have in the water, not by how alkaline (pH) the water is. 'Alkalinity increaser' products are prevalent in the hot tub industry, though they do have an effect on pH. If you are in the market for an alkalinity increaser, the most common is sodium bicarbonate. As for 'alkalinity decreaser' products, they will be an acid like sodium bisulphate (PH MINUS)
The role of total alkalinity in water chemistry
If you’re a pool or hot tub operator, you probably already know that pH can fluctuate up and down. And when it does, the pool or spa is constantly fighting against you. Having the right level of total alkalinity is a good thing, because it helps to keep the pH stabilized. Another way to think of total alkalinity's role is that it neutralizes acid, (acts as a buffer)!
You could have a ton of 8.3pH Sodium Bicarb floating around in the water, and have the same pH as if you added a smaller amount of 13.0pH soda ash. But the total alkalinity would be higher for the Sodium Bicarb, because there’s simply more of it in the water.
How to increase total alkalinity
If you want to increase total alkalinity in a pool or spa you need to know the fluid capacity of the vessel and your pH! It helps to have an accurate dosing calculator. Raising alkalinity is as simple as adding carbonates, bicarbonates or hydroxides to the water. Two of the most common pool products are sodium carbonate (soda ash) and sodium bicarbonate (sodium bicarb).
How to lower total alkalinity
You can lower alkalinity using acid. Some experts recommend a "acid column pour" to lower alkalinity, but we do not. In our experience--and indeed, scientific experiments back this up--column pouring is no more beneficial than dilution. We recommend diluting the acid in a bucket of water, and evenly pouring it around the pool or spa! Besides, column pouring can severely lower the pH in a concentrated location , which can throw the LSI off, and in turn, etch the surface.
Maintain total alkalinity within the range of 80-120ppm for healthy hot tub chemistry. Use an alkalinity increaser like sodium bicarbonate to raise total alkalinity, or an acid (PH MINUS) to lower it. When using high-pH chlorines such Cal Hypo, (SHOCK CHLORINE) stay lower in the range, like 80-100ppm. For low pH chlorines like Trichlor, (STABILISED CHLORINE) 110-120ppm is where you want to be. Consult your test kit/strips.
Hope this helps you understand TA