What is the best way to lower alkalinity?

What is alkalinity?

Alkalinity refers to the ability of water to resist changes in pH. It is the measure of how much acid can be added to water before the pH drops significantly. Water with high alkalinity is described as “basic,” “alkaline,” or “hard.” Alkalinity acts like a buffer and keeps the water’s pH at a stable level.

The main chemicals that contribute to alkalinity are bicarbonates, carbonates, and hydroxides. Bicarbonates are the most common. When an acid is added to water, these chemicals neutralize it. The higher the alkalinity, the more acid is needed to lower the pH.

Why is high alkalinity a problem?

High alkalinity causes a few issues:

• Makes pH difficult to adjust – With lots of alkalinity, it takes huge amounts of acid to lower pH. This makes precise pH control nearly impossible.
• Promotes algae growth – Alkalinity provides carbon dioxide that algae need to grow. The higher the alkalinity, the more algae problems.
• Interferes with chlorine – Alkalinity binds with chlorine, making it less effective as a sanitizer. More chlorine is needed to reach proper sanitation levels.
• Creates scale – Alkalinity contributes to scale formation on pool surfaces. This buildup clogs filters and requires acid washing to remove.

For these reasons, most pools target an alkalinity of 80-120 ppm. With alkalinity in this range, pH is easy to adjust, algae has less food, chlorine works better, and scale is minimized.

How to Test Alkalinity

You’ll need an alkalinity test kit to monitor levels. Test kits come in liquid drop, tablet, or digital formats. Follow the instructions with your kit to get an accurate reading. Here are a few tips:

• Collect a clean sample of water in a test tube
• Add the indicator solution from the kit – this changes color based on alkalinity
• View the color and match it to the color chart to find the ppm
• Rinse the tube between tests and re-cap reagents to preserve shelf life
• Test alkalinity weekly to stay on top of fluctuations

Digital photometers offer the highest accuracy, while liquid drop tests are the most affordable option.

How to Lower High Alkalinity

If alkalinity creeps above 120 ppm, use these methods to lower it:

Partial Drain and Refill

Draining some pool water and replacing it with fresh water is the quickest way to dilute alkalinity. This works best for minor 10-30 ppm adjustments. Calculate the amount of water needed to reach your target:

• Measure current volume and alkalinity level
• Determine new volume needed to dilute alkalinity to goal
• Drain the extra volume and refill with fresh water
• Retest alkalinity and repeat if needed

For example, a 20,000 gallon pool with 110 ppm alkalinity could be drained to 18,000 gallons and refilled to lower alkalinity to 100 ppm.

Acid Addition

Adding acid lowers total alkalinity by neutralizing the bicarbonates, carbonates, and hydroxides. Muriatic acid (hydrochloric acid) or sodium bisulfate are common choices. Use caution when handling acids!

Determine how much you need with an acid demand test:

1. Collect clean water sample and measure alkalinity
2. Add acid in small increments, retesting alkalinity after each addition
3. Stop when you reach the target alkalinity level
4. Multiply acid used by 4-5 to dose the entire pool

Add acid slowly in the deep end with the pump running. Retest after a few hours to see if further reduction is needed.

Carbon Dioxide Treatment

Dry ice (frozen carbon dioxide) lowers alkalinity when added to pool water. The carbon dioxide reacts with alkalinity to form carbonic acid which brings the level down. This is a more gradual, passive approach.

• Determine the pounds of dry ice needed based on water volume and alkalinity level
• Add dry ice slowly in shallow ends as it dissolves
• Retest and repeat treatments weekly as needed

Dry ice is simpler to use than liquid acids for homeowners. Just take safety precautions when handling.

Preventing High Alkalinity

It’s easier to prevent high alkalinity than continually fight to lower it. Here are some tips:

• Lower alkalinity in fill water – Adjust new water before adding to the pool. Aim for 80-100 ppm.
• Check alkalinity with additions – Test alkalinity after adding any chemicals or supplements as they can raise the level.
• Monitor calcium hardness – Keeping calcium in check prevents buildup of carbonates which increase alkalinity.
• Properly size the filter – Oversized filters fail to catch particles, adding to alkalinity over time.
• Replace filter media – Old, exhausted media dumps undesirable minerals into the pool. Swap it out regularly.
• Shock weekly – Oxidizing shock treatments destroy bicarbonates and carbonates that cause high alkalinity.

Staying ahead of alkalinity takes careful tracking and balance of all chemicals and minerals in the water.

Using a Water Softener

Water softeners remove minerals like calcium and magnesium that make water “hard.” Softened water is often recommended for pools since the lower mineral content makes balancing easier.

However, water softeners work by substituting the calcium and magnesium with sodium. This sodium can drastically increase alkalinity. Using softened water requires acidic adjustments to avoid escalating alkalinity.

Here are a few tips for managing softened water:

• Test alkalinity and pH frequently – Sodium affects both, so they’ll need monitoring.
• Use borates – They buffer against pH spikes better than carbonates and bicarbonates.
• Add acid – Have an acid handy to lower alkalinity when it creeps up.
• Limit cyanuric acid – It bonds easily with sodium, forming sodium cyanurate which boosts alkalinity.
• Watch saturation index – Sodium can impact the LSI and increase scale potential.

With extra precautions, softened water can be balanced for pool use. Alternatives like clarifying filters also remove hardness without affecting alkalinity.

Choosing Mineral Pools or Saline Systems

Mineral pools and salt chlorine generators add minerals to the water intentionally to achieve softened, gentle water for swimming. However, mineral levels require careful control to avoid alkalinity spikes.

Mineral Pools

Mineral pools use a combination of magnesium, potassium, and silver ions for water quality instead of harsh chlorine. However, the magnesium content raises hardness and pH, affecting alkalinity.

Tips for mineral pools:

• Start with low alkalinity water – Begin with softened water or a partial drain and refill.
• Limit magnesium dose – Add gradually and test frequently to ensure alkalinity stays in range.
• Balance pH last – Adjust alkalinity first, then calcium hardness. Finally balance pH.
• Shock regularly – Oxidizing shocks help control magnesium and mineral buildup.

Saline Pools

Saline chlorine generators use sodium chloride salt to produce chlorine through electrolysis. Like water softeners, the sodium content can quickly cause high alkalinity.

Recommendations for saline pools:

• Start low – Add salt gradually to avoid overshooting alkalinity.
• Use sodium bicarbonate – Baking soda buffers excess sodium better than sodium carbonate.
• Limit cyanuric acid – Again, it bonds with sodium and increases alkalinity.
• Adjust with acid – Have muriatic or sodium bisulfate acid on hand to reduce alkalinity.

With close monitoring and control of mineral and salt levels, you can reap the benefits of these systems without the alkalinity headaches.

Conclusion

High alkalinity is a common pool water challenge, but there are several effective methods to get it under control:

• Test alkalinity regularly and adjust when over 120 ppm
• Drain and partially refill the pool with fresh, low alkalinity water
• Add acids carefully to lower total alkalinity
• Use dry ice treatments to passively bring levels down
• Prevent alkalinity buildup through chemical balance and filter maintenance
• Adjust and monitor when using softened, mineral, or salt water

Balancing time and costs, acid addition or dry ice treatments offer reasonably quick reduction when alkalinity creeps up in a pool. Preventing spikes through regular shocks, replacing filter media, and controlling fill water are longer term solutions. With a little diligence, alkalinity can be managed for clean, balanced pool water.