Premium Japanese Oyster Shell Buffer Media (牡蠣殻 / Kakigara)

Bring a traditional Japanese approach to water management into your own setup with our Premium Japanese Oyster Shell Buffer Media (牡蠣殻 / Kakigara).

Used extensively by Japanese koi keepers and medaka breeders, natural oyster shells provide a gentle, long-lasting source of calcium carbonate that helps maintain stable water conditions while creating an excellent surface for beneficial bacteria and natural biofilm development.

Rather than relying on artificial additives, oyster shells work slowly and naturally, helping create the stable environment that fish thrive in.

Why Use Oyster Shells?

Natural oyster shells offer several benefits:

✓ Traditionally used in Japan for koi ponds and medaka keeping
✓ Helps naturally buffer water and maintain pH stability
✓ Contains over 96% calcium carbonate (CaCO₃)
✓ Slowly releases beneficial minerals into the water
✓ Supports beneficial bacteria and biofilm development
✓ Provides a natural alternative to artificial filter media
✓ Suitable for aquariums, breeding tubs, ponds and filtration systems

The naturally rough, porous surface of the shells provides an ideal area for colonies of beneficial bacteria to establish, supporting a healthy biological environment.

A Traditional Japanese Method (牡蠣殻 / Kakigara)

In Japan, oyster shells have been used for generations by fish keepers as a simple and natural way to support water quality.

The shells used are from the Japanese (Pacific) Oyster, a species widely associated with Japanese aquaculture. Their rigidity, biological stability and textured surface make them particularly valuable as both a natural mineral source and a habitat for beneficial microorganisms.

Many Japanese breeders prefer natural methods that gently support the ecosystem rather than making rapid chemical changes. Oyster shells fit perfectly into this approach, slowly influencing the water over time.

How Oyster Shells Work

Oyster shells are primarily made from calcium carbonate (CaCO₃). When placed in water, they gradually dissolve, helping to:

• Increase carbonate hardness (KH)

• Support pH stability

• Reduce sudden pH fluctuations

• Provide a source of calcium minerals

They are especially useful in:

• Soft water areas

• Rainwater-fed ponds

• Outdoor medaka tubs

• Breeding systems

• Aquariums requiring gentle buffering

Oyster shells are not a replacement for good filtration, water changes or responsible fish keeping. They are a natural supporting tool that works alongside a healthy ecosystem.

Recommended Use

Oyster shells work slowly, so it is best to start conservatively and adjust depending on your own water parameters.

Suggested starting guide:
5–10 g per litre of water

Examples:

• 4 litre container: 20–40 g

• 10 litre medaka tub: 50–100 g

• 20 litre tub: 100–200 g

• 50 litre pond: 250–500 g

• 100 litre pond: 500 g–1 kg

For medaka breeding tubs, many keepers prefer starting closer to 5 g per litre and increasing gradually if required.

The aim is stable, healthy water—not forcing the pH upwards.

How To Use

1. Rinse shells before use to remove dust and loose particles.

2. Place shells into the supplied reusable mesh media bag.

3. Position in your aquarium filter, pond filter, sump, or directly inside your breeding tub.

4. Allow the shells to work naturally over time.

The shells can remain in place for many months and may be replaced once they become thin or significantly reduced in size.

Premium Quality Natural Oyster Shells

Our oyster shells are:

• Sea washed

• Dried and cleaned

• Natural Pacific Oyster shell

• Over 96% calcium carbonate (CaCO₃)

• Suitable for freshwater use

Shell size:
Approximately 5–7.5 cm in length

As this is a natural product, shell shape, thickness and appearance will vary.

Approximate quantity:
1 kg contains around 40–50 shell pieces (guide only).

Available Pack Sizes

Choose the size best suited to your setup:

• 100 g – ideal for small aquariums and nano setups

• 250 g – suitable for smaller breeding tubs

• 500 g – ideal for several small tubs

• 1 kg – suitable for multiple medaka tubs or larger aquariums

• 2 kg – ideal for larger pond and breeding systems

Each retail pack includes a FREE reusable black drawstring mesh media bag for easy placement and removal. Choose either a 14cm x 10cm bag, or a 20cm x 15cm bag.

Suitable For

✓ Japanese Medaka (メダカ)
✓ Koi ponds
✓ Goldfish ponds
✓ Shrimp aquariums
✓ Freshwater aquariums
✓ Outdoor breeding tubs
✓ Biological filtration systems

Inspired by Japanese Fishkeeping Tradition

Simple, natural and effective.

From the Japanese breeder’s perspective, successful fish keeping is about creating balance. Oyster shells are a small piece of nature that helps support the invisible ecosystem around your fish—providing minerals, stability and a surface where life can develop.

A traditional method, used for generations, now available for modern medaka keepers.