Learning Objectives

By the end of this lesson, learners will be able to:

• Understand the purpose of each substrate layer in a bioactive vivarium.
• Identify the components of ABG mix and why it is the standard for dart frogs.
• Compare ABG to alternative substrate blends.
• Build a substrate layer that supports drainage, plant growth, and microfauna health.
• Recognise signs of a healthy vs. unhealthy substrate.

Lesson Content

The substrate is a fundamental part of a bioactive vivarium. It supports plants, shelters microfauna, regulates humidity, and forms part of the natural nutrient cycle. A good substrate must be:

• moisture-retentive
• airy
• resistant to compaction
• long-lasting
• plant-friendly
• microfauna-friendly

Dart frogs thrive when substrate conditions remain consistent and breathable.

1. What Makes a Good Bioactive Substrate?

A suitable substrate must:

• retain moisture without becoming waterlogged
• allow airflow to prevent anaerobic conditions
• provide structure for plant roots
• support decomposition through microfauna
• resist breaking down too quickly

A poor substrate becomes stagnant, muddy, or compacted—making it unsuitable for plants or microfauna.

2. ABG Mix: The Gold Standard

ABG stands for Atlanta Botanical Garden, which developed a recipe that has become the most widely used dart frog substrate worldwide.

Standard ABG Ingredients:

• Sphagnum moss (dried) – moisture retention
• Tree fern fibre – long-lasting aeration
• Ground orchid bark – structure & drainage
• Charcoal – improves air quality and reduces odours
• Peat moss – retains moisture

Typical ABG Ratio:

(All parts by volume)

• 2 parts sphagnum
• 1 part tree fern fibre
• 1 part orchid bark
• 1 part charcoal
• 1 part peat

ABG is extremely long-lasting, often functional for 3–5 years before replacement.

3. ABG Benefits

• Maintains moisture gradients
• Never compacts excessively
• Supports a huge microfauna population
• Excellent root support for terrarium plants
• Doesn’t break down quickly
• Helps stabilise humidity
• Works with both LECA and false bottoms

This is why ABG is the standard in dart frog keeping.

4. Alternative Substrate Blends

Some keepers create custom blends using available materials.
Here are the most common alternatives:

(1) “Tropical Bioactive Mix” (Homemade)

Popular blend with similar performance to ABG.

Typical recipe:

• Coconut fibre (50%)
• Orchid bark (20%)
• Sphagnum moss (20%)
• Horticultural charcoal (10%)

Pros:

• Easy to source
• Cheaper than ABG

Cons:

• Breaks down faster
• Can compact if too much coco fibre is used

(2) “Forest Floor” Mix

Used for large enclosures and high-humidity tanks.

Typical ingredients:

• Compost-free soil
• Coco husk chips
• Sphagnum
• Leaf mould
• Microbark

Pros:

• Mimics natural forest substrate
• Excellent for plant-heavy tanks

Cons:

• Less predictable
• Must avoid any compost/fertilisers

(3) Soil-Based Mixes (With Caution)

Some plant-heavy tanks use soil-based mixtures.

Only safe if:

• organic
• compost-free
• fertiliser-free
• pesticide-free

Not recommended for beginners.

5. Depth of Substrate Layer

Dart frog vivariums require a deep enough substrate for:

• plants
• microfauna
• moisture retention

Recommended depth:

5–10 cm, depending on vivarium height.

Tall enclosures benefit from deeper substrate to support large roots.

6. Adding Sphagnum, Mosses & Additives

Sphagnum (long-fibre) can be:

• mixed into the substrate
• placed on top for moisture retention
• used to anchor plants
• relied on for humidity buffering

Additives often used:

• Earthworm castings → mild nutrient boost
• Bark mulch → microfauna shelter
• Coco chips → structure

Avoid fertilisers — dart frogs are highly sensitive.

7. Signs of a Healthy Substrate

A good substrate will:

• smell fresh and earthy
• spring back when pressed
• feel moist but not soggy
• show gradual decomposition in leaf litter
• support visible microfauna activity
• allow roots to spread without rot

8. Signs of Unhealthy Substrate

• muddy or compacted consistency
• strong sour or rotten smell
• water pooling at the surface
• yellowing or dying plants
• visible anaerobic black patches
• microfauna population decline

If these occur, the substrate mix or moisture balance needs correction.

Key Takeaways

• ABG is the gold standard for dart frog bioactive substrate.
• Good substrate must hold moisture while staying airy.
• Alternative mixes work but require more maintenance.
• Substrate should typically be 5–10 cm deep.
• Healthy substrate smells earthy, supports roots, and houses active microfauna.