Ammonia (NH3) is highly toxic to fish, but in minute concentrations, it is the preferred nitrogen source for plants. However, violent spikes in ammonia cause chemical burns and osmotic destruction of delicate plant tissues. This phenomenon is extremely common during the first weeks of starting an aquarium when heavily fertilized active soils (like ADA Aqua Soil Amazonia) are used, which intentionally release massive amounts of ammoniacal nitrogen to feed carpeting plants. If the pH is alkaline (above 7.0), ammonium (NH4+) converts into the more lethal ammonia (NH3), worsening the burns.

Leaf tips and growing apices turn black, translucent, and rot (melt). New leaves emerge curled, deformed, or necrotic. Adventitious roots can burn, turning dark. Combined with strong lighting, an ammonia spike will inevitably and simultaneously trigger an explosion of Green Water (Volvox) or diatoms on the injured plant surfaces.

Setting up a new tank with 'rich' active soils without performing the massive water changes required by the protocol. The death of a large hidden animal rotting in the tank. Immature or suddenly collapsed biological filter (e.g., after washing filter media in chlorinated tap water or heavy antibiotic treatments).

Massive water changes. During the first month with active soils like ADA Amazonia, it is mandatory to change 50% of the water every day for the first week, every two days in the second week, and so on, precisely to dilute excess ammonia. Using high-quality liquid nitrifying bacteria will accelerate biofilter establishment, converting lethal NH3 into more tolerable nitrates (NO3).

Start the tank by scrupulously following the water change protocols indicated by the substrate manufacturer. If the aquarium is populated, monitor values regularly with liquid reagent tests. Maintaining a slightly acidic pH (around 6.5) via CO2 injection drastically reduces ammonia toxicity by transforming it into the ammonium ion, which is much more harmless.