Tap water is convenient, but in hydroponics it can silently sabotage plant growth. Most developed countries add chlorine or chloramines to drinking water to keep it safe, and while these disinfectants protect humans, they can seriously harm roots, beneficial microbes, and overall plant health.

In this blog we break down why dechlorination matters, how chlorine differs from chloramines, and the best ways to make your water truly plant-friendly.

Chlorine vs. Chloramines: What’s in Your Water?

Free Chlorine

• Added by water utilities as a basic disinfectant
• Evaporates naturally in 12–24 hours
• Can be accelerated with aeration
• Easy to remove — but less commonly used today

Chloramines (Mono-, Di-, Tri-chloramines)

• More stable disinfectants increasingly used worldwide
• Do NOT gas off, even after days or weeks
• Persist in nutrient tanks and foliar sprays
• Can significantly reduce plant growth and kill beneficial microbes

This is where many growers get caught out: letting water sit out removes chlorine, but not chloramines.

Why Chlorine and Chloramines Hurt Hydroponic Plants

Research consistently shows significant reductions in plant growth when reactive chlorine compounds are present.

Harmful effects include:

1. Root Damage

• Browning
• Reduced nutrient uptake
• Enzyme disruption

2. Destruction of Beneficial Microbes

Chlorine kills:

• Mycorrhizal fungi
• Trichoderma
• Bacillus species
• Other free-living microbial partners

These microbes directly support nutrient availability, root protection, and growth acceleration—so losing them comes at a cost.

3. Imbalanced Microbial Ecosystems

Even low levels can disturb the biological balance in substrates and reservoirs.

Important Clarification: Chlorine ≠ Chloride

Chloride salts (e.g., calcium chloride, sodium chloride) are not disinfectants.
They are cheap, poor-quality fertilizer ingredients — but they don’t sterilize roots the way chlorine gas does.

When we talk about dechlorination, we mean reactive chlorine species, not chloride ions.

Why “Letting Water Sit Out” Doesn’t Work Anymore

Aerating or storing water for 24 hours only removes free chlorine, not chloramines.

Modern tap water often contains:

• 0.2–1 mg/L chlorine
• Even more in North America, especially during heat waves
• Higher doses in summer when bacterial growth risk increases

Water companies increase chlorine for human safety — not plant health. As a result, chlorine levels peak precisely when growers irrigate most frequently.

Dechlorination Methods: Pros & Cons

Below are the most practical options for hobbyists and commercial hydroponic growers.

1. Natural Gassing Off

✅ Cost-free
✅ Removes free chlorine
❌ Ineffective against chloramines
❌ Time-consuming (12–24 hours minimum)

Not recommended if chloramines are present — which is true in most regions.

2. Ascorbic Acid (Vitamin C)

✅ Neutralises chlorine instantly
✅ Effective against chloramines
✅ Safe for plants
❌ Adds acidity (pH adjustment needed)
❌ Short shelf life (oxidises to orange/brown)

Works well if used fresh and measured correctly.

3. Dedicated Dechlorination Products

(e.g., Eutrema’s Dechlorinator, sodium-free formulas)

✅ Instantly neutralises chlorine & chloramines
✅ Affordable
✅ Treats large volumes of water
✅ No sodium (important!)
❌ Additional product to buy if not included in your nutrients

A reliable and popular choice for hydroponic growers.

4. Fertilizers With Built-In Dechlorination

(e.g., Gold Leaf in the US, Liquid Gold in the UK)

✅ Instantly dechlorinates on contact
✅ Includes pH management, biostimulants, and chelated nutrients
✅ Zero extra steps
❌ Premium price point

This is the most convenient option — ideal for growers who want a one-bottle solution from seed to harvest.

You can verify this yourself using DPD tablets:

• Chlorinated water turns pink
• Add Gold Leaf/Liquid Gold → turns clear/yellow instantly

5. Carbon Filters & Reverse Osmosis

✅ Removes chlorine, chloramines & heavy metals
✅ Produces extremely clean water
✅ Great for sensitive crops
❌ Costly
❌ Requires installation
❌ Increases need for CalMag supplementation
❌ RO waste water

Best for advanced growers or large installations.

6. Rainwater Harvesting

✅ Naturally chlorine-free
✅ Soft, slightly acidic
✅ Favoured by many farmers

But…

❌ Risk of pathogens (e.g., Pythium, Phytophthora)
❌ Heavy metals from roofs (zinc, lead)
❌ Mosquito larvae and algae
❌ Legality varies by region
❌ Storage infrastructure required

Rainwater is great if stored hygienically and legally — otherwise, proceed with caution.

✅ So What’s the Best Choice?

For most hydroponic growers:

⭐ Use a sodium-free dechlorinator
— OR —
⭐ Switch to a nutrient with built-in dechlorination (Gold Leaf / Liquid Gold)

If you want ultra-pure water:

⭐ Reverse osmosis (then add Cal-Mag back in)

Avoid:

❌ Water softeners (add sodium — toxic to plants)
❌ Relying only on aeration
❌ Long-term storage of ascorbic-acid solutions
❌ Roof runoff with questionable materials

Why Dechlorination = Higher Yields

Dechlorinating your water is one of the most overlooked ways to improve plant:

• Growth rate
• Nutrient uptake
• Microbial health
• Stress resistance
• Final yield and quality

It’s an easy, additive upgrade to any system — and often produces results growers can see within weeks.

Final Thoughts

Dechlorination might not be the flashiest topic in hydroponics, but it’s one of the most impactful. Whether you’re growing leafy greens, fruiting crops, ornamentals, or medicinal plants, removing chlorine and chloramines is a simple step that can dramatically boost results.

If you want help choosing the right method for your setup, feel free to ask — I can recommend a tailored solution.

Article by Dr Russell Sharp

If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:

Hydroponics Daily Podcast: https://podcasts.apple.com/us/podcast/hydroponics-daily/id1788172771

Cereal Killers Podcast: https://podcasts.apple.com/us/podcast/cereal-killers/id1695783663