Beneficial Bacteria Are Essential

We were hesitant to title this post “No Water Change: between myth and reality” for there is not a more deep-rooted belief amongst fish keepers that the necessity to perform regular water change. All fish tanks have this in common: they generate nitrates, and diluting nitrate level is the primary reason for changing water. There are a few other circumstances (next post) for this routine. But instead, we switched our focus to providing suggestions and directions to help maintain healthy colonies of beneficial and essential bacteria.

Nitrifying bacteria

Nitrogen is one of the most common elements on earth. While most elements are generally stable, nitrogen undergoes a natural transformation process through oxidization called nitrification converting N2 into ammonia (NH3) or ammonium (NH4) if pH is lower than 7, and ammonia into nitrites (NO2-). In the last step, nitrites is converted into nitrates (NO3-). These steps are made possible by nitrifying bacteria: Nitrosomonas and Nitrosoccocus (NH3 => NO2- ) and Nitrobacter, Nitrospina, Nitrococcus and Nitrospira (NO2- => NO3-).

Nitrosomas and nitrobacter species are present in any cycled aquarium. They grow by consuming organic matter such as food leftover and fish waste and inorganic nitrogen compounds by benefiting from existing or/and self-producing enzymes, proteins and the presence of oxygen. Without these bacteria, fishkeeping would be impossible as ammonia and nitrite are lethal to the aquatic life we keep.

These bacteria are present virtually everywhere, although some aquarists resort to bacterial products to boost their presence and diversity.

Denitrifying bacteria

Although much less toxic than ammonia and nitrites, nitrates are the primary reason for changing water frequently (every week or other week). Heavily stocked aquarium would require a 30% water change while lightly stocked aquarium would require a 10% water change, the average being 20%. Four parameters will in fact determine the frequency and volume of water change:

         Sensitive aquatic lives, including young fish and fry, corals (…)

         Stocking density

         Filtration system


Elevated nitrates level will affect the aquatic life and also promote algae growth.

Seldom present in aquariums but common in nature, denitrifying bacteria are remarkably adapted to many conditions and use nitrate as their primary food source to produce energy. More common than we are aware of, the denitrifying process is a group work involving several species to reduce nitrate to molecular nitrogen or inert nitrogen gas.

There is a myth or perhaps just a misunderstanding, but it is so entrenched into many “hardcore” hobbyists that it has taken the allure of a myth, is that these bacteria do not survive in an aquarium because of the amount of oxygen circulating in an aquarium. The vast majority of aquarium does not have enough oxygen to disturb these bacterial colonies. However denitrifying bacteria need a surface to attach to and air-stones or protein skimmers or a strong water flow will make it more difficult for these bacteria to reach their “settlements”.

Denitrifying bacteria do not come naturally in an aquarium, they need to be added, and because of their sensitive nature and slow growth rate, in large quantity. The foremost condition for their presence is space. Aerobic bacteria will colonize filters, be present in water and settle on rocks. Anaerobic may choose the same areas but will prefer substrates.

Optimizing denitrifying bacteria’s presence

An entire article could be dedicated on the topic. As noted previously, denitrifying is a group work. If denitrification is not occurring at a sufficient rate in an aquarium, it may be because conditions are allowing other processes bacteria use to create energy to dominate instead. Two of these pathways are fermentation and respiration.

To promote denitrification over respiration and fermentation, certain steps can be taken:

  • Make sure a clean biofilter is used when adding AquaBella.
  • Remove as much organic content (that can result in promoting fermentation over denitrification) as possible through vacuuming the substrate’s surface. Do not (important) vaccum the substrate in its depth, that will disturb the established anaerobic colonies. To aerate the substrate, take a stick and gently move it tracing lines.
  • Bring water flow down to 3 times the volume of the aquarium per hour.
  • Turn off protein skimmer, air stone and UV sterilization equipment for a week to allow bacteria to settle.

In case the above is not sufficient and nitrates are still present, you could:

  • Add biofiltration media. This may be useful for aquariums that show only a short-term denitrification effect, as this indicates the AquaBella microbes aren’t attaching and colonizing in parts of the aquarium with lower oxygen content, allowing for the desired long-term effect. (Highly recommend PureMedia from Cermedia). This will also provide more surface for AquaBella microbes to attach and colonize.
  • Add a carbon source (vodka), which can also promote anaerobic and facultative bacterial growth.

2/3 of AquaBella Bio Enzyme's content is comprised of different strains of bacteria that one way or another contribute to the denitrification process. 

Marc Thibault