What Is The Best Water Hardness For Plecos?

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Keeping Plecos is pretty straightforward; these fish are considered hardy and can manage various water conditions.

But what about water hardness? Which range do they prefer? How can you adjust it to their preference? And what happens if the water is too soft or too hard?

In this article, I’ll address all these questions and many more, so you leave with all the information you need. Let’s dive right into it.

What Is The Best Water Hardness For Plecos?

Plecos generally thrive in slightly soft to moderately hard water. The ideal water hardness range for most Plecos is between 4 to 15 dH (degrees of hardness).

However, specific requirements may vary depending on the species.

  • Diverse Origins: Plecos originate from South American rivers with varied water hardness. The Panaque nigrolineatus, for instance, prefers water softer than a common bristlenose Pleco.
  • Health and Vitality: Maintaining water hardness ensures Plecos’ health. Inconsistent levels can cause stress, diseases, and a shortened lifespan.
  • Breeding Considerations: For breeding Plecos, specific hardness is key. The Zebra Pleco, for example, requires softer water for successful reproduction.
  • Species Variance: Not all Plecos have the same requirements. While many thrive in 4-15 dH, some might prefer conditions outside this range.

To break it down further, here’s a selection of Plecos with their respective water hardness ranges:

Pleco TypeWater Hardness
Common Pleco (Hypostomus plecostomus)5-15 dH
Bristlenose Pleco (Ancistrus spp.)6-10 dH
Zebra Pleco (Hypancistrus zebra)4-7 dH
Panaque nigrolineatus (Royal Pleco)4-8 dH
Snowball Pleco (Hypancistrus inspector)5-10 dH
Gold Nugget Pleco (Baryancistrus xanthellus)5-12 dH
Clown Pleco (Panaqolus maccus)6-10 dH
Rubber Lip Pleco (Chaetostoma formosae)5-10 dH
Vampire Pleco (Leporacanthicus galaxias)5-12 dH
Whiptail Pleco (Rineloricaria spp.)6-10 dH
Blue Phantom Pleco (Hemiancistrus sp.)5-12 dH
King Tiger Pleco (Hypancistrus sp.)5-10 dH
Butterfly Pleco (Dekeyseria spp.)6-10 dH
Peppermint Pleco (Parancistrus nudiventris)5-10 dH
Medusa Pleco (Ancistrus ranunculus)6-10 dH
Sultan Pleco (Leporacanthicus joselimai)6-10 dH
Red Fin Cactus Pleco (Pseudacanthicus fordii)5-12 dH
Giant Otocinclus (Hypoptopoma gulare)4-8 dH
Flash Pleco (Panaqolus albivermis)6-10 dH
Spotted Orange Seam Pleco (Pseudolithoxus anthrax)5-12 dH

Also Read: Plecos Water Parameters

Rubber Lip Pleco (Chaetostoma formosae)

How Do I Measure the Water Hardness in My Pleco Tank?

To measure the water hardness in your Pleco tank, you’ll need a water hardness test kit commonly sold in pet or aquarium stores.

These kits usually contain a test tube, reagent, and a color chart.

By adding the reagent to a water sample and comparing the resulting color to the chart, you get the hardness value.

  • Test Kit Components: Most kits include a test tube where you’ll add tank water, then drop in the provided reagent. The water’s color will change based on hardness.
  • Reading Results: Once the reagent is added, the water color will shift. Match this color to the provided chart to determine the hardness level.
  • Digital Testers: Advanced aquarists might prefer digital hardness testers. Simply dip into the tank, and they’ll provide an immediate reading.
  • Professional Assistance: If unsure, some local aquarium stores offer water testing. They can confirm your results, ensuring the best for your Plecos.

My recommendation: Premium Water Hardness Test Kit (link to Amazon).

How Can I Increase the Water Hardness for My Plecos?

If the water hardness is too low, simply follow these steps:

1. Add Calcium Carbonate (Crushed Coral)

Calcium carbonate, often sourced from crushed coral, gradually elevates water hardness when introduced to the tank.

  • Natural Method: By adding 1-2 pounds of crushed coral per 10 gallons, you can mimic the mineral-rich environments where Plecos thrive.
  • Gradual Increase: Crushed coral’s slow dissolution means a safer, consistent rise in hardness over weeks, ensuring no sudden changes that might stress your Plecos.
  • Aesthetic Appeal: Incorporate crushed coral as a substrate layer or within a filter bag in your tank’s filter to both enhance visual appeal and function.

My recommendation: Estes Crushed Coral for Aquarium (link to Amazon).

2. Use Mineral-rich Substrates

Incorporating substrates rich in minerals can naturally elevate the water’s hardness.

  • Choosing the Right Type: Look for substrates labeled as “African Cichlid Mix” or those specifically made for hard water tanks; they release calcium and magnesium into the water.
  • Application Amount: For effective results, replace or mix your current substrate with the mineral-rich type, ensuring a depth of at least 2 inches.
  • Monitoring: After the switch, test water hardness weekly to ensure it’s increasing at a pace suitable for your Plecos.

My recommendation: Carib Sea African Ivory Sand for Aquarium (link to Amazon).

3. Use Hard Water Conditioners

Water conditioners designed for hard water can raise the mineral content.

  • Read the Label: Always follow the recommended dosage on the product; typically, it’s a few drops per gallon.
  • Consistent Application: Apply during water changes, ensuring even distribution for uniform hardness across the tank.
  • Compatibility: Ensure any conditioner you choose is safe for Plecos and other tank inhabitants.

4. Dissolve Seashells in the Tank

Seashells can be a decorative and functional addition to your tank, releasing calcium carbonate.

  • Preparation: Thoroughly clean and boil seashells before adding them to prevent contaminants from entering the tank.
  • Placement: Scatter them on the substrate or position them as decorative pieces, ensuring they’re fully submerged.
  • Regular Checks: Monitor the seashells for erosion over time and replace as necessary to maintain the desired hardness for your Plecos.

5. Add Commercial Hardness Boosters

These are products designed specifically to increase the hardness of tank water.

  • Choose Wisely: Opt for reputable brands and ensure they’re Pleco-safe. Each product might have different concentrations and effects.
  • Follow Instructions: Typically, you’d add a certain amount per gallon during water changes, but always refer to the product’s label.
  • Monitor Effectiveness: Use your hardness test kit to check the results after application, ensuring it’s within the ideal range for your Plecos.

How Do I Decrease the Water Hardness for My Plecos?

On the other hand, if the water hardness in your Pleco tank is too high, there are several ways to reduce it:

1. Perform Regular Water Changes with Soft Water

Swapping out some of the hard water in your tank with softer water during regular water changes is a straightforward method.

  • Routine Checks: Regularly measure your tank’s water hardness using a test kit to monitor levels and determine how much soft water to introduce.
  • Adjustment Ratios: Begin with a 20% water change using soft water, and observe the hardness reduction. Adjust this ratio in future water changes to reach desired levels for Plecos.
  • Consistency: Maintain a consistent schedule, as abrupt changes can be stressful for Plecos.

2. Use Reverse Osmosis (RO) Water

RO systems filter out a significant portion of the minerals, producing soft water ideal for Plecos.

  • Efficiency: RO systems can remove up to 99% of water impurities, ensuring consistently soft water for your tank.
  • Mixing Strategy: For best results, mix RO water with tap water in a 50:50 ratio, adjusting based on the desired hardness.
  • Maintenance: Regularly check and replace RO membranes to keep the system effective for the sake of your Plecos.

3. Add Peat Moss to the Filter

Peat moss naturally softens water by releasing humic substances that bind to calcium and magnesium ions.

  • Preparation: Before adding, boil the peat moss to eliminate potential contaminants and make it sink more easily.
  • Quantity: Around a cup of boiled peat moss in a filter bag for a 50-gallon tank can effectively reduce hardness; adjust amounts based on your tank size.
  • Regular Replacement: Change the peat moss every 4-6 weeks to ensure it continually softens the water for your Plecos.

4. Use Commercial Water Softeners

These are products designed to lower water hardness and are available at most aquarium stores.

  • Reliable Brands: Opt for trusted brands and ensure the product is safe for Plecos, as some might contain undesirable chemicals.
  • Dosage: Always adhere to the manufacturer’s guidelines; generally, a few drops per gallon during water changes should suffice.
  • Monitor Impact: Continuously check water hardness post-application to ensure it remains in the ideal range for Plecos.

My recommendation: API WATER SOFTENER PILLOW (link to Amazon).

5. Collect Rainwater for Water Changes

Rainwater, being naturally soft, can be a good alternative for reducing tank hardness.

  • Safety First: If collecting rainwater, ensure it’s free from pollutants. Using a clean collection system and avoiding the initial runoff helps keep it pure for Plecos.
  • Storage: Store collected rainwater in clean, dark containers to prevent algae growth before introducing it to the tank.
  • Consistent Use: Mixing rainwater and tap water in a fixed ratio during changes ensures a steady water condition favorable for Plecos.

What Happens If I Keep Plecos in Inappropriate Water Hardness?

Keeping Plecos in inappropriate water hardness can lead to several health and behavioral issues.

Inconsistent hardness can cause physiological stress, hamper healthy growth, and decrease their overall lifespan.

  • Stress Indicators: Plecos show stress through erratic swimming and reduced appetite; improper hardness weakens their immunity.
  • Growth Challenges: Incorrect mineral balance can stunt growth, particularly in juvenile Plecos, leading to potential deformities.
  • Skin and Scale Issues: Plecos’ skin and scales can deteriorate in wrong hardness levels, leading to vulnerability and infections.
  • Reproductive Problems: Plecos in non-ideal water conditions may have reduced fertility and face challenges in successful breeding.
  • Shortened Lifespan: Consistent exposure to unsuitable hardness can reduce the overall lifespan and vitality of Plecos.

Also Read: Best pH For Plecos


For those of you in a rush, here’s a short summary:

  • The ideal water hardness for most Plecos falls within the range of 4 to 15 dH, although specific requirements may vary among species.
  • Maintaining consistent water hardness is crucial for Plecos’ health and vitality, as fluctuations can lead to stress, diseases, and a shorter lifespan.
  • Different Pleco species have varying hardness preferences, making it essential for aquarists to research and meet the specific needs of their chosen species.
  • To measure water hardness in a Pleco tank, aquarists can use test kits or digital testers, ensuring the water conditions are suitable for their Plecos.
  • When adjusting water hardness, aquarists can either increase it using methods like crushed coral or mineral-rich substrates, or decrease it with techniques such as water changes with soft water or the use of reverse osmosis water.