Chapter 2 — Viable Environments | Holobiont Aquarium Theory

Chapter 2

Viable Environments — Parameter Flexibility

Applicable configurations and their options

2.1 Configuration Flexibility

The mandatory requirements for this theory to function are limited; other elements can be freely chosen.

Requirements

Overflow system (oxygen supply via splash aeration, large sump)
Porous media in sump (bacterial colonization surface)
Regular carbon source dosing (C:N ratio maintenance)
Detritivorous organisms (biomass consumers)

With requirements met, the following parameters can be freely chosen.

Parameter	Options	Effect
Substrate	Fired akadama (+peat moss), Oiso gravel, coral sand, bare tank	Determines pH lock equilibrium
Detritivores	Daphnia, Tubifex, Gammarus, Neocaridina, Loach, etc.	Size determines full-auto viability
Circulation	Full-auto / Manual / Large pump	Maintenance effort
Carbon source	Ethanol, acetic acid, sucrose, etc.	Different decomposition rates
Main tank	Planted / bare / large tank	Theoretically applicable to all

2.1.1 Substrate Material Selection

The substrate material is the parameter that determines the pH lock equilibrium point. Since the primary bacterial colonization surface in this theory is the porous media in the sump, the substrate functions to set the pH baseline. The sump media must be porous, but if this condition is met, the same material as the substrate can be used.

Fired Akadama + Peat Moss

pH 5.5〜6.5

Tannic and fulvic acids from peat moss leach out, lowering pH. Does not disintegrate; long-term viable

Chocolate gourami, Apistogramma, and other ultra-soft, weakly acidic species

Fired Akadama

pH 6.7〜6.9

Weakly acidic, porous with good bacterial colonization. Long-term viable

Tetras, angelfish, and other weakly acidic fish

Oiso Gravel

pH ~7.0

Neutral, stable, long-term usable. Slightly alkaline if shell content is high

Goldfish, medaka, and fish preferring neutral to mildly alkaline

Bare Tank

pH ~7.0

No substrate. pH equilibrium depends on sump media. Easy maintenance

Large carnivorous fish, training purposes, etc.

Coral Sand

pH 8.0〜8.4

Strongly alkaline. Calcium carbonate dissolution continuously raises pH

Marine fish, African cichlids, brackish fish, etc.

2.1.2 Types and Properties of Carbon Sources

Carbon sources are the energy source for bacteria, with different decomposition rates depending on type. Since the nitrogen source (NH₄⁺) is rate-limiting, excess carbon is dissipated as CO₂, making precise measurement unnecessary. However, extreme overdosing can degrade water quality, so adjusting dosage based on pH trends is recommended.

Ethanol
C₂H₅OH

Ethanol → Acetic acid → TCA cycle

Fast

Acetic Acid
CH₃COOH

Supplied directly as acetic acid

Medium

Sucrose
C₁₂H₂₂O₁₁

Sucrose → Hydrolysis to monosaccharides

Slow

This theory uses a "carbon source extract" mixing multiple carbon sources. This mitigates the risk of rapid bacterial proliferation and oxygen consumption while achieving stable continuous supply. Specific recipes are explained in Chapter 3.

2.1.3 Benthos Selection and Full-Auto Conditions

The selection of detritivorous organisms (benthos) directly affects the degree of circulation automation. For the full-auto method, benthos must be small enough to pass through the supply pump impeller.

Daphnia

0.2〜3mm Full-auto

Directly filter-feeds suspended bacteria. High water quality improvement effect, ideal live food for small fish. Also serves as dissolved oxygen indicator

Tubifex

〜2mm Full-auto

Fast reproduction rate, easy to supply stably. Highly palatable to fish

Gammarus

2〜10mm Full-auto

Also effective at substrate agitation. Many fish readily prey on them

Asellus (Water Louse)

5〜15mm Full-auto

High detritus decomposition ability. Tolerant of low temperatures, stable reproduction in freshwater

Malaysian Trumpet Snail

1〜3cm Manual (substrate agitation)

Burrows into substrate during day preventing anaerobic conditions. Feeds on detritus at night. Substrate agitation function aligns with "non-anaerobic substrate" consequence

Neocaridina Shrimp

1.5〜3cm Full-auto

Broadly feeds on detritus, algae, and bacterial biomass. Short reproduction cycle with constant supply of juveniles. Easy to obtain

Amano Shrimp

3〜5cm Manual / Large pump

Detritus decomposition ability stronger than Neocaridina. Can process larger organic matter.Does not breed in freshwater, so population does not naturally increase

Loach

5〜15cm Manual / Large pump

Strong substrate agitation. Ideal as food for large carnivorous fish

Full-Auto Criteria If the pump impeller clearance is approximately 3mm or more, passage of Tubifex and juvenile Gammarus is often possible. However, checking pump specifications in advance is recommended.

2.1.4 Difficult-to-Apply Configurations

While this theory has broad applicability, the following configurations make it difficult to meet mandatory requirements (sufficient oxygen supply, large sump).

× HOB filter alone: Lacks a large-capacity processing chamber equivalent to a sump, unable to secure space needed for bacterial biomass accumulation and benthos proliferation.

× Canister filter alone: Sealed structure provides insufficient internal oxygen supply. Cannot maintain long-term growth conditions for aerobic heterotrophic bacteria.

※ Tanks under 30L: Not technically impossible, but bioload and carbon source management become extremely demanding. Recommended only after gaining sufficient experience.