Pool alkalinity: how to regulate it to prevent algae and maintain pH
The forgotten parameter that ruins the maintenance of many pools
Many pool owners are familiar with pH and chlorine, but few pay attention to the total alkalinity of the water. However, alkalinity is actually the parameter that controls everything: without stable alkalinity, pH constantly fluctuates, chlorine loses effectiveness, and algae find the ideal environment to proliferate. In other words, you can adjust the pH ten times a week and never achieve balanced water if alkalinity is not within its correct range.
In this article, we explain exactly what alkalinity is, what happens when it's out of range, why it's key to preventing green algae, and how to raise it correctly and naturally. Everything you need to know to stop fighting with your water and start enjoying your pool.
What is the total alkalinity of pool water?
Total alkalinity (TA) measures the concentration of carbonates, bicarbonates, and hydroxides dissolved in water, expressed in parts per million (ppm) or mg/l. In practical terms, it acts as a pH buffer: it absorbs acidic or basic changes introduced by chlorine, rain, treatment products, or swimmer waste, preventing the pH from rising or falling sharply.
The best analogy to understand its function is that of a mattress: the more alkalinity the water has, the harder it is for the pH to change due to any external disturbance. Thanks to this stability, all other treatment products also work more efficiently, and less of each is consumed.
The difference between alkalinity and pH: a very common mistake
Although closely related, alkalinity and pH are not the same and are not corrected with the same products. pH measures the acidity or basicity of water on a scale of 0 to 14. Alkalinity, on the other hand, measures the water's capacity to resist pH changes, i.e., its stability. It is perfectly possible to have an apparently correct pH but low alkalinity, and in that case, the pH will fluctuate constantly throughout the day even if adjusted correctly every morning.
Imagine that pH is the temperature of a room and alkalinity is the thermal insulation of the walls. You can regulate the heating as much as you want, but if the walls have no insulation, the temperature will continuously vary with every window opening or external change.
Similarly, if alkalinity is low, pH will fluctuate with every rain, every swimmer, and every product you add, making it impossible to keep it stable. Therefore, correcting alkalinity before pH is not an optional step, but the only approach that works in the long term.
The optimal alkalinity range and what happens outside of it
The recommended total alkalinity range for a domestic pool is 80 to 120 ppm. Within this margin, the pH remains stable, and the other water parameters are much easier to control. Outside this range, however, problems quickly cascade.
Very low alkalinity
⚠️ Dangerous
Low alkalinity
⚠️ Unstable
Optimal range
✅ Ideal
High alkalinity
⚠️ Problems
Very high alkalinity
⛔ Critical
Symptoms of alkalinity out of range
- pH fluctuates constantly
- Green algae appear easily
- Chlorine is consumed very quickly
- Water can become corrosive
- Eye and skin irritation for swimmers
- Pitting or discoloration of walls and liner
- pH rises and is resistant to dropping
- Water becomes milky or cloudy
- Scale and limescale on walls, filter, and equipment
- Chlorine loses effectiveness
- Increased consumption of corrective products
- Filter clogs more frequently
The relationship between low alkalinity and the appearance of green algae
Green algae is one of the most frustrating problems in pool maintenance, and low alkalinity is one of its main triggers. To understand why, it's necessary to follow the chain of cause and effect:
How low alkalinity favors algae proliferation
- Alkalinity falls below 80 ppm, either due to rain, intensive use, or simple natural consumption of water.
- Consequently, the water's pH begins to fluctuate unpredictably, rising and falling by several tenths throughout the day.
- When the pH rises above 7.6, the available free chlorine drops dramatically: at pH 8.0, only 20% of the added chlorine is active as a disinfectant.
- With reduced disinfecting capacity, microscopic algae in suspension are not eliminated and begin to multiply exponentially.
- Within 24-48 hours, the water turns greenish, and within a few days, visible green algae appear on walls, steps, and the bottom.
Therefore, when green algae appear recurrently, the definitive solution is not to add more chlorine, but to stabilize alkalinity first. Without that basis, any algaecide treatment is temporary, and the problem will return again and again.
Many owners react to green algae by adding large amounts of chlorine or algaecides, which visually solves the problem but does not address the root cause. If alkalinity remains low, pH will continue to fluctuate, chlorine will remain ineffective, and green algae will return in a matter of days or weeks.
The correct sequence is always: correct alkalinity → stabilize pH → add necessary chlorine or algaecide. In this way, the treatment is long-lasting, and product consumption is significantly reduced.
Why low alkalinity is so common in summer
Although alkalinity can drop at any time, summer concentrates all the factors that consume it the most. Knowing them helps anticipate the problem before green algae appears:
Factors that reduce water alkalinity
- Rain: rainwater has an acidic pH (between 5.5 and 6.5 in most of Spain) and virtually no alkalinity. Each rain dilutes the alkalinity of the pool water and acidifies the environment.
- Intensive use: sweat, cosmetics, and urine from swimmers are acidic and consume alkalinity continuously during peak usage days.
- Liquid and tablet chlorine: sodium hypochlorite and trichlorine tablets have a very low pH. Each time chlorine is added, some alkalinity is consumed to buffer the acidic impact.
- pH reducing products: muriatic acid and other acidic pH correctors lower both pH and alkalinity simultaneously if used excessively.
- Intense evaporation: summer heat increases evaporation, and the water added to replenish the level can have very different alkalinity depending on its origin.
During peak season (June-September), it is recommended to measure alkalinity at least once a week with a complete test kit or specific test strips that include total alkalinity measurement.
After heavy rains or periods of very intensive use, it is advisable to take an additional measurement within 24 hours to detect drops before the imbalance has visible consequences.
How to naturally raise pool alkalinity
Once the problem is identified, the next step is to correct it properly. Puerto Verde's natural alkalinity enhancer is the safest and most effective way to do this without resorting to harsh chemical compounds.
The correct order: always alkalinity before pH
This point is fundamental and deserves special emphasis. Before adding any pH corrector, you must ensure that alkalinity is in range. If the pH is raised with low alkalinity, the corrected value will not last more than a few hours, and the adjustment will have to be repeated continuously. In contrast, with alkalinity stabilized between 80 and 120 ppm, the pH remains stable with minimal, infrequent adjustments.
Step-by-step: how to apply the alkalinity enhancer
- Measure current alkalinity with a test kit or test strips. Note the value and calculate how much you need to raise it to reach the optimal range (80-120 ppm).
- Consult the product's dosage to know the exact amount according to your pool volume and the required alkalinity increase. As a guideline, to raise 10 ppm in a 50 m³ pool, approximately 500 g of product is needed.
- With the recirculation pump running, dissolve the calculated amount in a bucket with pool water before pouring it in. This ensures a more homogeneous distribution and avoids localized concentrations.
- Pour the solution slowly around the entire perimeter of the pool, distributing it evenly along the edges.
- Leave the recirculation active for at least 4-6 hours for the product to be completely distributed throughout the pool.
- After this time, measure alkalinity again. If it is still below 80 ppm, repeat the process with an additional smaller dose. Never add the entire correction at once if a large increase is needed.
- Once alkalinity is in range, wait at least 24 hours before measuring and correcting pH. This allows alkalinity to stabilize completely, and the pH correction will be more precise and long-lasting.
If alkalinity is very low (below 50 ppm), it's tempting to add all the necessary correction at once. However, a sudden increase in alkalinity can cause the pH to rise uncontrollably and generate a "pH rebound" effect that is difficult to correct.
Therefore, it is most advisable to make partial corrections: raise alkalinity in steps of 20-30 ppm, wait 4-6 hours between each addition, measure, and repeat until the optimal range is reached. This is a slower but much more controlled and effective process.
Once alkalinity is corrected: how to properly raise pH
With alkalinity stabilized within its optimal range, correcting pH is a much simpler and more predictable process. The goal is to keep it between 7.2 and 7.4, which is the range where chlorine works with maximum efficiency and the water is most comfortable for swimmers.
Why pH drops after correcting alkalinity
It is common for the pH to rise slightly above 7.4 or even 7.6 when adding the alkalinity enhancer. This is normal and should not be a concern: it is due to the buffering effect of the added bicarbonates. In most cases, the pH stabilizes on its own within the correct range in the following hours as the CO₂ in the water balances with that in the atmosphere.
Therefore, it is always advisable to wait at least 24 hours after alkalinity correction before measuring the pH and deciding if it needs correction. This avoids unnecessary corrections that generate a counterproductive cycle of adjustments.
When it is necessary to raise pH
- When the pH is below 7.2 after stabilizing alkalinity and waiting 24 hours.
- After adding large amounts of liquid chlorine, which is very acidic and can significantly lower the pH.
- At the beginning of the season, when the pool is filled with tap water that in many areas has a slightly acidic pH.
- After heavy rains, once alkalinity is corrected and the water has mixed well.
Reference table: quick diagnosis of your pool water
To simplify diagnosis and know what action to take in each case, here is a quick reference table with the most common symptoms and their most probable cause:
| Observable symptom | Most probable cause | Solution |
|---|---|---|
| Greenish water or green algae | Low alkalinity → unstable pH → ineffective chlorine | Correct alkalinity → adjust pH → chlorine shock |
| pH rises on its own shortly after correction | Alkalinity too high | Reduce alkalinity with diluted muriatic acid |
| pH drops on its own in a few hours | Alkalinity too low | Raise alkalinity with natural enhancer |
| Milky or cloudy water without algae | High alkalinity + high pH → calcium precipitation | Reduce alkalinity and pH + natural flocculant |
| Chlorine is consumed very quickly | pH too high or unstable alkalinity | Correct alkalinity → adjust pH to 7.2-7.4 |
| Eye and skin irritation after swimming | pH out of range or chloramines due to imbalance | Stabilize alkalinity → adjust pH → flocculant |
| Scale or limescale on walls and skimmer | High alkalinity and pH | Gradually reduce both parameters |
Why choose a natural alkalinity enhancer
Not all alkalinity enhancers on the market are the same. Conventional ones often contain additives, stabilizers, or impurities that, although effective in raising alkalinity, can introduce unwanted compounds into the water that are especially problematic for sensitive skin.
Puerto Verde's natural alkalinity enhancer, on the other hand, is formulated with natural ingredients, without synthetic chemical additives, and manufactured in Spain. Furthermore, being completely biodegradable, it generates no toxic waste when the pool is emptied at the end of the season.
| Feature | Puerto Verde natural enhancer | Conventional enhancers |
|---|---|---|
| Composition | Natural ingredients, no additives | Mixtures with stabilizers and additives |
| Safety for sensitive skin | ✅ Completely safe | ⚠️ Variable depending on composition |
| Environmental impact | 100% biodegradable | Partially biodegradable |
| Effectiveness | Very high | Very high |
| Manufacturing | Spanish, with traceability | Variable, often imported |
| Residues in water | None | Possible accumulative stabilizers |
Frequently asked questions about pool alkalinity
Below we answer the most common questions about alkalinity and its correction in domestic pools:
What is total alkalinity in a pool and why does it matter?
Total alkalinity measures the water's ability to resist pH changes, acting as a buffer that absorbs acidic or basic disturbances. When it's in the optimal range of 80-120 ppm, the pH remains stable and chlorine works at maximum efficiency. When it's outside that range, the pH fluctuates unpredictably, chlorine is consumed faster, and conditions become favorable for the proliferation of algae and slime.
What is the difference between alkalinity and pH?
They are related but distinct parameters. pH measures the acidity or basicity of water on a scale of 0 to 14. Alkalinity, on the other hand, measures the stability of pH, i.e., its resistance to change. It is possible to have an apparently correct pH with low alkalinity, and in that case, the pH will constantly fluctuate throughout the day. Therefore, alkalinity should always be corrected first, and then pH, never the other way around.
Why does slime appear even if I add chlorine regularly?
Because chlorine only works well in a narrow pH range: between 7.2 and 7.4. If alkalinity is low, the pH fluctuates and can easily rise above 7.6. At that pH, chlorine loses much of its disinfectant effectiveness, and algae find an ideal environment to proliferate, even if there is chlorine in the water. The definitive solution is to stabilize alkalinity, not to add more chlorine.
How often should I measure and correct alkalinity?
During swimming season, it is advisable to measure alkalinity at least once a week, along with pH and free chlorine. After heavy rains or periods of very intensive use, an additional measurement should be taken within 24 hours. If alkalinity is consistently within the optimal range, the correction frequency can be extended to once every two weeks.
Can I raise alkalinity and pH at the same time?
It is not recommended to do so simultaneously. The correct order is: first raise alkalinity to the optimal range (80-120 ppm), wait 24 hours for it to stabilize, and then measure the pH. In many cases, by correcting alkalinity, the pH already settles into the correct range on its own or needs only minimal adjustment. Trying to correct both parameters at once makes it difficult to control the process and often leads to unexpected fluctuations.
How long does it take for alkalinity increaser to take effect?
Puerto Verde's natural alkalinity increaser dissolves quickly in water and starts acting from the very first moment. However, for alkalinity to be homogeneously distributed throughout the pool and for the value to stabilize, it is necessary to keep recirculation active for at least 4-6 hours after application. After that time, you can measure again and decide if you need a second correction.
Where can I buy natural alkalinity increaser for pools?
You can purchase our natural alkalinity increaser at puertoverde.es, available in different formats with shipping throughout Spain. It is also available on Amazon with Prime shipping if you prefer that option.
⚗️ Does your pool need more stability?
100% natural alkalinity increaser · No chemical additives · Spanish manufacturing · Shipping throughout Spain
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