Isn't nitrification inhibited below pH 6?Updated a month ago

A persistent myth in the aquarium hobby claims that tanks cannot cycle below pH 6, or that bacterial oxidation of ammonia stops when pH drops below a certain level. While commonly known ammonia-oxidizing bacteria such as Nitrosomonas and Nitrosococcus function best at higher pH ranges, they are not the only ammonia oxidizers in aquatic systems. In acidic environments, archaea, thaumarchaeota, and other organisms take over the role of primary ammonia oxidizers. These microbes that operate in acidic environments take longer to propagate and settle in compared to Nitrosomonas and Nitrosococcus, which operate more optimally in alkaline environments.

Many natural lakes and rivers have pH ranges below 6 (some in the 3+ range) and thrive with microbial life.

APT Balance includes non-typical strains of microbes that thrive in lower pH environments. In tanks with aquasoil (lower pH) the added bonus is that almost all ammonia exists as ammonium (NH4+), which is non-toxic.

For further reading on low pH and bacteria interactions head here.

Aquasoil CO2 injected aquariums in soft water countries tend to have naturally low pH values. In our 4ft setup above, the pH hovers between 5.0 (when CO2 is at peak saturation) and 6.2 (When CO2 is turned off).