Understanding the Role of Beneficial Bacteria in Aquariums

After setting up a new tank with water, turning on the filter, and reaching the right temperature, the missing component is the beneficial bacteria. These bacteria will inhabit the filter, live in the substrate, and cover the tank's decorations and glass. The nitrogen cycle will then begin. Fish waste breaks down into ammonia, which is highly toxic to fish. The first stage of the nitrogen cycle involves building a colony of "Nitrosomonas bacteria" to convert ammonia into nitrites. These bacteria naturally occur in water but in very low concentrations, insufficient for a new tank. They are lithotrophic bacteria that thrive on clean, hard surfaces like filter media, tank decorations, and glass. Besides needing ammonia as a food source, they also require a good supply of oxygen to grow and multiply. To establish a large enough colony in your aquarium, you can use one of two methods: fishless cycling, where you add drops of pure ammonia to the water to feed the bacteria, or lightly stocking the tank with a few fish to produce ammonia through their waste. Decaying matter and uneaten fish food also produce ammonia but can impact overall water quality. During the expansion of the bacteria colony, you might notice bacterial blooms causing the water to appear milky. Once the colony is well-established, the water will clear. Algae may also grow in the aquarium as it uses ammonia as a food source.

Converting Ammonia to Nitrites and Nitrates

Our colony of Nitrosomonas bacteria has now grown large enough to handle all the ammonia in the tank, converting it into nitrites. While nitrites are less toxic than ammonia, they are still harmful to fish. To address this, another type of bacteria, known as Nitrobacter, will start to establish itself in the filter and aquarium. These bacteria convert nitrites into nitrates. The Nitrobacter bacteria perform a similar role to Nitrosomonas but deal with nitrites instead. Like Nitrosomonas, they need nitrites as their food source and require oxygen to thrive, which must be provided by the aquarium owner. At this stage, ammonia levels should be almost zero, but resist the urge to add more fish. Adding more fish will increase ammonia levels again, slowing down the growth of Nitrobacter, which thrive only at low ammonia levels. Once the Nitrobacter colony is established, both ammonia and nitrite levels should be close to zero. Nitrate levels will rise but can be controlled with regular water changes. Even if test kits show some nitrate, they are generally not immediately toxic to your fish.

With thriving colonies of Nitrosomonas and Nitrobacter bacteria in your filter and aquarium, it's essential to maintain their health. These bacteria need oxygen to survive, so it's important to clean the filters regularly to prevent clogging. Always rinse filters with old tank water rather than fresh water, as fresh water can kill most of your beneficial bacterial colonies.

The balance between bacterial colonies is crucial. Adding too many fish at once can disrupt this balance and cause mature aquariums to experience mini-cycles. During these mini-cycles, Nitrosomonas bacteria may need to rebuild their population to manage ammonia levels, preventing them from hindering the growth of Nitrobacter colonies.

Bacteria Cultures Sold in Stores

There are bacterial cultures available for purchase, marketed as products that can “kick start” your filters. However, opinions are divided on their effectiveness. Some aquarists praise these products, while others question whether suppliers can successfully bottle a live bacterial colony and sustain it with enough food and oxygen to keep the bacteria viable until use.

We've already discussed the importance of beneficial bacteria, but it's equally important to be aware of harmful bacteria that can enter your aquarium. These harmful bacteria often thrive in areas like the substrate if gravel or sand is not cleaned regularly. Such bacteria can introduce diseases and infections to your fish, so it’s vital to take precautions to minimize their introduction. Harmful bacteria can be introduced by your hands coming into contact with fish food, during tank maintenance when your hands are in the water, or through a lack of regular cleaning, allowing detritus to build up in the substrate and water. Washing your hands before maintenance and feeding is a simple yet effective step - avoid using soap, as it can contaminate your tank water!

Quarantining new fish before adding them to your tank can help you spot potential infections before they spread. Nothing is more devastating than introducing a single sick fish that could potentially wipe out your entire stock.