Ammonia is the thing that kills fish. This takes it out.

Every fish excretes ammonia and every uneaten pellet decays into more of it. A biofilter converts it eventually. In the meantime — in warm water, after a feed, after a grading, or in a young system whose bacteria are not established — ammonia climbs faster than the bacteria can handle.

In laboratory measurement, clinoptilolite removed 80.8% of total ammonia nitrogen in 24 hours at 1 ppm, outperforming activated carbon. In a European recirculating system growing Arctic charr it cut ammonium by 22.7% and nitrite by 16.7% during a period of elevated feed rate. In a granular biofilter, total nitrogen removal reached 94% against 79% for activated carbon.

It is also the medium that maintains itself. Nitrifying bacteria colonise the outside of the grains and strip the ammonium off as fast as it binds — measured as roughly three times more effective than chemical regeneration, with no chemicals at all. The bed does not need replacing on a schedule.

In slurry and digestion the same chemistry pays differently. Stored pig slurry lost 59% of its supernatant ammonium nitrogen and 88% of its chemical oxygen demand, most of it within two hours. In published work on poultry-manure digestion, 10 g of natural zeolite per litre raised methane production by 109.75% by relieving ammonia inhibition.

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What has actually been measured

• 80.8% of total ammonia nitrogen removed in 24 hours, at 1 ppm, outperforming activated carbonlaboratory measurement
• Ammonium −22.7%, nitrite −16.7% in a cold-water recirculating system growing Arctic charrLithuania, at elevated feed rate
• 94% total nitrogen removal in a granular biofilter, against 79% for activated carbonpublished comparison
• +109.75% methane from poultry-manure digestion at 10 g/LKougias 2013