Can You Use Hard Water for Discus? {How To Soften Your Discus Tank Water}

Aare you wondering if your Discus fish will survive and remain hardy in hard water? Can you use hard water for discus?

Is hard water beneficial or harmful for Discus fish?

In this article, we’ll discuss if you can use hard water for your Discus fish.

Can You Use Hard Water for Discus?

Discus fish do not prefer hard water. Soft, acidic water between a 7.0-8.0 pH with a hardness of 18-70ppm (1°-4° dKH) is ideal under temperatures of 82°-89° F.

What Is Water Hardness?

When we are referring to water hardness in a Discus tank, we are speaking specifically about the concentration of dissolved minerals in the tank water.

These minerals are predominantly:

  • calcium
  • magnesium
  • carbonate

The higher the mineral concentration, the harder the water will be. You can test water hardness in the following ways:

1. General Hardness (GH)

With general hardness, we are checking the amount of calcium and magnesium present in the water

2. Carbonate Hardness (KH)

Also known as Alkalinity, we are checking for the amount of carbonate or bicarbonate ions.

  •  1 dGH = 17.84 ppm
  • 1 dKH  = 17.86 ppm

Discus Water Hardness PPM

Water Requirements for Discus

  • Discus prefer acidic, warm, soft water.
  • Hardness should range from 1° to 4° dKH
  • pH should be between 6.0 and 7.0. (18 to 70 ppm).
  • Even though wild Heckel discus like water around 90° F, the temperature should be regulated between 82° and 86° F.

Can Discus Live in Hard Water?

No. In my experience, pH values between 6.8 to 7.6 are ideal for discus, whether they are wild-caught or captive-bred.

The same is true for water hardness; discus can often handle gentle to medium hardness.

German-bred discus are known for tolerating higher pH and harsher water.

What Should The Water Hardness Be For Discuss Fish?

1. Soft water measures at:

  • 0 – 4° or 0 – 75 ppm

2. Moderately hard measures at:

  • 4° – 8.5° or  75 – 150 ppm

3. Hard water measures at:

  • 8.5° – 17° or  150 – 300 ppm

4. Very hard water measures at:

  • over 17°or over 300 ppm

Your Discus fish are not adapted to hard water. They would prefer soft, acidic water with a hardness of 18-70ppm or 1°-4° dKH.

Which Fish Live In Hard Water?

Hard water fish include many livebearers. Here is list of fish who live in hard water in captivity and in the wild.

  • African Cichlids
  • Guppies
  • Mollies
  • Platies
  • Swordtails
  • X Ray Tetras
  • Rainbowfish
  • Killifish
  • Freshwater Gobies
  • Paradise Fish
  • Archer Fish 
  • Mono Fish
YouTube video

How Do I Soften The Water In My Discus Tank?

There are a few methods to softening the water in your Discus tank, but it’s important to exercise a lot of caution. The parameters as a whole must not fluctuate or it will stress your Discus fish more than slightly hard water.

Start with the following tips to soften your aquarium water:

  1. Test the GH, KH and pH readings with test kits. They must not be fluctuating. Test the water more than once per day for 1-3 days.
  2. Soften the water very gradually and slowly.
  3. Use collected rainwater that is soft naturally.
  4. Mix rainwater with tap water if it’s too soft.
  5. Ensure that rainwater is not contaminated and not collected near polluted, industrial areas.
  6. Use water softening pillows to absorb calcium, magnesium and metal ions.
  7. Water softening pillows don’t work at well in tanks larger than 30 gallons. This works for juvenile Discus, but not adults in 75 gallon tanks.
  8. Try peat moss as filter media. It will bind calcium and magnesium ions through chelation and demineralization.
  9. Soak peat in boiling water, then let it cool to kill off any possible contaminants.
  10. Place driftwood in the tank to neutralize carbonate compounds by releasing tannic acid.
  11. Use RO (reverse osmosis) water. Purchase an RO/DI system or bring RO water to your home in large containers.

Why Will Happen to My Discus Fish in Hard Water?

Discus fish in captivity can handle hard water in varying amounts when placed in community tanks. They may not thrive and rising stress levels are concerning. Here are some issues that can arise:

  • inability to breed
  • susceptible to disease 
  • discoloration or paleness
  • lowered immune system
  • lethargy 

Can I Use Water Softeners In My Discus Tank?

Water softeners are meant to protect appliances from limescale build-up leading to breakdowns. They are not meant to soften aquarium water.

Is water softener safe for aquariums? No. They exchange minerals with sodium, but do not help your fish in any way. Save the water softeners for pipes, shower doors, dishwashers and washing machines.

What Are The Most Common Soft Water Fish?

Some of the most popular fish in captivity that thrive in soft water as as follows:

  • Discus 
  • Apistogramma 
  • Rasboras
  • Dwarf Gouramis 
  • Neon Tetras
  • Barbs 
  • Angelfish 
  • Cory Catfish

A reverse osmosis filter would be the safest and easiest way to reduce water hardness for your Discus fish and tankmates that prefer soft water.

Can My Discus Fish Breed In Hard Water?

No. Your Discus fish will not be able to breed in hard water. These fish have lived and survived in soft, acidic water.

Discus fish can tolerate hard water in captivity in many cases, but they need soft water to spawn or lay eggs.

Can European Discus Breed In Hard Water?

There is evidence to suggest that European bred Discus Fish in hard water can breed. They have been tank bred for many generations and have slowly become adapted to it.

Asian or Wild Discus fish are not adjusted to hard water. They will not breed if the water is not slightly acidic and soft. A reverse osmosis filter will help soften their water if you wish for them to breed.


We have offered may tips to soften your aquarium water, but this is not an emergency situation. Your Discus fish require the water parameters to remain steady and fluctuations resulting from the pressure to soften your water may lead to more stress and health issues.

Gradual softening though reverse osmosis is the preferred method to help your Discus fish live in tank conditions that mimic their natural water in the wild.


Thanks for visiting for this  article on Discus fish. We have many more related article that you can check out. We care about your aquatic life and we’re here to help. Bye for now!

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.