pH & Alkalinity in a Hot Tub or Spa
Today's post is hopefully a simple post, although it can be a complicated topic. pH and Alkalinity are close cousins in water chemistry, each affecting and affected by, the other.
pH is a measurement of how acidic (below 7.0) or basic (above 7.0) - your hot tub water is. Alkalinity is a measurement of the amount of carbonates and bicarbonates in the water, which acts as a buffer to help stabilize pH.
When pH is LOW (below 7.0), the water becomes corrosive to seals, gaskets and plastics. When pH is HIGH, the water can produce scale, leading to cloudy spa water or deposits of calcium on surfaces and inside pipes.
Lower pH by adding Spa pH decreaser, or sodium bisulfate.
Raise pH by adding Spa pH increaser, or soda ash.
When Alkalinity is LOW, this causes pH to "bounce" or change easily - you may raise the pH, but it only lasts for a few hours. When Alkalinity is HIGH, this makes it hard to adjust pH in the first place, it makes pH very resistant to change.
Lower Alkalinty by adding Spa pH decreaser, or sodium bisulfate.
Raise Alkalinity by adding Spa Alkalinity increaser, or sodium bicarbonate.
The problem is... trying to adjust alkalinity without affecting pH, or vice versa. Fact is, you can't - since they are both so closely related - but there are some tricks up my sleeve.
- To Lower Alkalinity more than pH, add the pH decreaser with the spa pump off
- To Lower pH more than Alkalinity, add the pH decreaser with the spa pump on
- To Raise Alkalinity more than pH, use Alkalinity Increaser, with the spa pump off
- To raise pH more than Alkalinity, use pH Increaser, with the spa pump on
Another problem is... overdosing the spa or hot tub, and swinging the pH and Alkalinity far to the other extreme. Know your hot tub size in gallons, and refer to the label for dosage per 100 gallons.
Dosage is almost always just a capful or two, a few ounces - so be careful not to over-shoot the mark! Add a small amount and retest the water after 30 minutes, and if needed, re-dose again.
When lowering alkalinity, you may have to raise the pH again afterwards, just slightly, which may also raise your alkalinity again just slightly. In some cases, where alkalinity has drifted very high, over 150 ppm - you may need to make many adjustments - sort of a two steps forward, one step back kind of thing...
TIP: When buying pH and Alkalinity adjustment products for your spa - there's no need to overspend. We have all of the major spa chemical brands, and also a lower priced house brand of spa pH and alkalinity chemicals.
TIP: Don't use Pool Chemicals in your Hot Tub. Chemically, pH and alkalinity adjustment chemicals are the same, but the labeling is for a pool 100x larger, which makes it quite easy to over or under dose, even if you are good at math!
Keep at it! It's important to have correct spa pH and alkalinity, both for protection of spa equipment and surfaces, and so that your sanitizer works most effectively.