Can I Use Pool PH Down for Plants? (Explained)

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Key Takeaways:

  • Pool pH down contains sodium phosphate or similar compounds, which are not recommended for plants.
  • While some growers report success with pool pH down for hydroponics, it is not food grade and carries risks.
  • Specialized pH down products designed for plants, like phosphoric acid, are recommended over pool chemicals.
  • When adjusting pH, use care as acids/bases can be dangerous if used improperly.
  • Start with small amounts of pH down, test after 15-30 minutes before adding more to avoid overshoot.

What is Pool pH Down and Why is it Used??

Pool pH down, also known as pH decreaser or acid demand, is a chemical product used to lower the pH of swimming pool water. It contains an acidic compound such as sodium bisulfate (NaHSO4) or sodium phosphate (Na2HPO4). Pool service technicians use pH down to counteract the natural tendency of pool water to drift upwards on the pH scale over time due to factors like evaporation and the presence of contaminants.

Keeping the pH within an ideal range between 7.2 – 7.8 is critical for effective pool sanitization, preventing corrosion or scale build-up, maximizing chlorine efficiency, and protecting swimmer comfort. If the pH rises too high (becoming too alkaline), chlorine disinfecting ability is reduced. pH down provides a convenient method to restore proper acidity quickly through the addition of the acidic buffer.

Why is Pool pH Down Not Recommended for Plants??

While pool pH down is great for adjusting swimming pool water chemistry, it is generally not recommended for use in gardens or for hydroponic plant growth. There are a few key reasons why it is better to avoid using pool pH down on plants:

Not Food Grade: Pool chemicals are not held to the same purity standards as agricultural chemicals. Pool pH down is industrial-grade and may contain impurities not intended for consumption. There could be traces of manufacturing contaminants like cleaning solvents, heavy metals from pipes, or other unknown elements that could potentially be harmful if absorbed by edible plants.

Too Strong: Pool pH down is designed for rapidly lowering pH in thousands of gallons of water, so it is far more concentrated than most plant-safe acids. It would be easy to overshoot and burn plants by applying too much pool acidifier. It lacks the buffering capacity to prevent drastic pH swings.

Salt Accumulation: Common active ingredients like sodium bisulfate and sodium phosphate can leave behind sodium salts that build up over time with repeated use. Excess salts can damage plant roots and soil structure.

Not Cost Effective: Pool pH down is relatively expensive compared to acids specifically formulated for horticulture use. Specialty hydroponic pH down optimized for plants would provide better value.

Lack of Nutrients: Unlike some hydroponic pH adjusting products, pool pH decreaser does not contain any added macronutrients or micronutrients to benefit plant growth and flowering. It simply alters acidity without providing fertilization.

Has Pool pH Down Been Used Successfully on Plants??

While not recommended, some hydroponic gardeners have reported using dilute solutions of pool pH down to alter nutrient reservoir acidity with varying degrees of success. Often very small amounts are tested to avoid burning plants with the caustic industrial acid. In hydroponics and other soilless systems, the effects of salt buildup are reduced, though long term use still carries risks.

One 2013 study from the University of Arizona tested effects of pool pH decreaser in hydroponic lettuce production. They found it was able to effectively lower pH without immediately damaging plants, however long term impacts were not evaluated [1]. Though possible to use pool pH down in very controlled hydro environments, purpose-made plant acids are still greatly preferred.

What are the Dangers of Using Pool pH Down on Plants??

Because pool pH down is not designed for horticultural use, there are some significant dangers associated with using this chemical product on garden and hydroponic plants:

  • Burning: Too much pool acid too quickly can readily burn and damage plant tissues. Finding the right dilutions takes trial and error.
  • Toxicity: Impurities or manufacturing contaminants could potentially leach into edible plants, causing health issues if consumed. Further research is needed on toxicity.
  • Environmental Harm: Improper disposal of leftover pool chemicals could pollute groundwater, endanger helpful soil biology, or otherwise disrupt outdoor growing ecosystems.
  • Equipment Damage: Pool acid products may be corrosive to irrigation lines, hydroponic system components, and other equipment not built for industrial acids.
  • pH Crash: It is easy to overshoot desired pH leading to an abrupt crash that further endangers roots and disrupts nutrient availability.
  • Lack of Control: Without precise buffering capacity, pH can fluctuate widely between dangerously low and potentially too high.

Using pool chemicals like pH down outside their intended purpose is risky. While anecdotes of success exist, horticultural acids designed for plants are the far safer choice.

What pH Down Options are Recommended for Plants??

Instead of pool acid, there are many pH down products specifically formulated for adjusting acidity in gardens, hydroponics, and other growing systems. Some better options include:

Phosphoric Acid – A food-grade mineral acid that readily lowers pH in water or nutrient solutions. It provides phosphorus as an added nutrient. Dilute carefully as it is still corrosive at high concentrations.

Nitric Acid – This strong mineral acid is sometimes used as it contributes bioavailable nitrogen along with acidity. It must be handled with great care as nitric acid is highly corrosive.

Citric Acid – Made naturally from citrus fruits, citric acid is a weaker organic acid commonly used as a food additive. It slowly breaks down and has very low toxicity.

pH Down mixes – Many pre-mixed products combine citric, phosphoric, or nitric acid with buffers and nutrients tailored for hydroponics.

Double Buffer Acids – Specialized products utilize a two-component buffer system to precisely control pH decrease. They prevent overshoot and fluctuating acidity.

With many options available formulated for plant use, pool pH decreaser is not needed. Look for hydroponic acids that are food-grade, provide secondary nutrition, and offer enhanced control over pH change. Follow all label precautions.

How Should pH Down Be Used on Plants Safely??

When applying any type of acidifier to lower pH for plants, proper usage and safety precautions are critical. Here are some tips for safely using pH down in gardens and hydrosystems:

  • Read labels thoroughly and follow recommended dilutions. Start with weaker dilutions until familiar with a new product.
  • Wear skin, eye, and respiratory protection when handling pH down concentrates to avoid chemical burns. Work in a well-ventilated area.
  • Acidify water/nutrients in a separate container first before adding to a reservoir. Never add straight chemicals to an active system.
  • Test current pH before adding any acid to know how far you need to adjust downwards.
  • Go slowly – only adjust pH 0.1 or 0.2 at a time, allowing 15-30 minutes between applications and retesting.
  • Have a base like potassium hydroxide or sodium bicarbonate available to neutralize solutions if acidity overshoots.
  • Dispose of all waste properly without pouring in groundwater, sinks, or other environmental systems.

Adjusting acidity can be dangerous if proper care is not taken, regardless of whether using pool, horticultural, or food-grade products. Patience, planning, safety gear, and small iterative changes will lead to success altering pH for plants.

Frequently Asked Questions About Using Pool pH Down on Plants

Is it okay to use just a little pool pH down on my vegetables?

No, it is not recommended to use pool pH chemicals of any amount on edible plants. Even small concentrations could potentially introduce manufacturing contaminants into food products. Stick with food-grade acids designed for crops.

What concentration of pool pH down would be safe for plants?

There is no recommended “safe” concentration, as pool chemicals are not designed for crops. Extreme dilution may reduce burning risks but does not eliminate potential toxicity or long term buildup issues. Purpose-made plant acids are vastly preferred.

My indoor hydroponic plants seem fine after using pool pH down – so it’s safe, right?

Not necessarily – while some growers have used highly diluted pool acidifiers without acute issues, long term impacts are unknown. Buildup of sodium and impurities could still occur. It is not considered safe practice.

Instead of buying hydroponic pH down, isn’t it cheaper to use pool chemicals?

While pool acid may seem superficially cheaper, horticultural-grade products designed for plants provide far better pH adjustment, control, and nutrition for plants. Any perceived savings disappear when factoring risks and results.

How quickly will pool pH down start burning my plants if I use too much?

Burning can begin within minutes to hours after applying overly concentrated pool acid products. Always start very dilute and increase concentration slowly only after testing effects. Burning or toxicity symptoms may take time to fully show.


While pool pH down contains acidic compounds capable of adjusting water acidity, this industrial-grade product carries significant risks when used for plants. Possible toxicity, accumulation of contaminants and salts, and dangers of burning mean it is not recommended for gardens or hydroponics. Specialized pH adjusting acids designed for plants, crops, and hydroponic systems are vastly preferable. When managing pH, always exercise caution by starting slowly and diluting acids appropriately. Used properly, pH down is a safe tool – but pool chemicals should be avoided in favor of horticultural options better suited to plants.

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