5.1 Discussion and Outlook

5.1.1 Applicability to Large Tanks

In larger tanks, the increased water volume provides a greater water quality buffer, making fluctuations less likely. The expanded habitat for bacteria and detritivorous organisms is expected to improve system stability. While conventional water-change-based management becomes "more difficult to maintain as tanks grow larger," this theory may reverse that relationship.

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5.1.2 Limitations and Unverified Aspects

• This study is based on a single system only; verification of reproducibility remains a future task
• The effect of different substrate materials on pH lock is a theoretical prediction; no empirical testing has been conducted with aqua soil or coral sand
• There are no operational examples using larger detritivores such as loaches
• Application to planted layout tanks (ADA-style, etc.) has not been verified, but is theoretically considered applicable

5.2 Conclusion

This paper proposed the Holobiont Aquarium Theory, which achieves a no-water-change system for freshwater aquariums by combining carbon assimilation of ammonia by heterotrophic bacteria with nitrogen cycling through food chains mediated by detritivorous organisms, and reported one year of empirical results.

The core of this theory consists of the following two points:

1. Elevated C:N ratio through carbon source addition → Direct ammonia assimilation by heterotrophic bacteria → Nitrification bypass
2. Biomass consumed by detritivores → Consumed by carnivorous fish in main tank → Nitrogen cycles within the food chain

This theory is independent of parameters such as detritivore species, substrate material, and circulation method, and is considered applicable to various environments. Further verification and feedback are welcomed.

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Author: Institute of Biological Environmental Engineering
ver.11 / March 2026

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