Cycling Your Freshwater Aquarium

Let's Get Cycling!

We aquarists spend months mulling over our choices regarding our future fish paradises. We ponder what size tank to buy, what type of lights to add, which color substrate do we want, and what fish should we stock. If you are anything like me, you will nit pick each part to purchase and then stalk your UPS man waiting for everything to arrive. Then you have to wait patiently/impatiently to add the fish to your set up.  Luckily for me, I have Mrs. Krill to keep me from immediately adding every creature directly into our tank. She frequently repeats the mantra, “patience is more than virtue in this hobby”. Although I hate to admit it, she does have a point. If you rush this last step then all of the preparations and planning will be for naught.

Unfortunately not everyone has a Mrs. Krill of their own and it is far too common for beginner aquarists, who don’t understand the nitrogen cycle, to add large amounts of animals into their newly established aquarium.  In their enthusiasm, rookie aquarists may not realize that their new tank needs to be cycled. Uncycled tanks experience what is referred to as “New Tank Syndrome” and witness a die off of aquarium inhabitants. Cycling a tank prevents an aquarium inhabitant purge (i.e., large die off).  Cycling in the aquaria world refers to the nitrogen cycle and how bacteria will turn fish waste (ammonia) into nitrite and then finally to less toxic nitrate that we, the aquarist, can remove from our tank by doing water changes. An uncycled tank will cause a buildup of ammonia or nitrite which is harmful for fish. To avoid this build up, bacteria colonies need to be established within the aquarium to move these harmful elements through the nitrogen cycle.

​Luckily for us, bacteria exists everywhere and readily reproduces given the right conditions. Factors such as temperature and food availability can impact how quickly bacteria reproduce. Nitrifying bacteria experience optimum growth between temperatures of 77 - 86 F (25 - 30C). You can add these beneficial bacteria by introducing media from established aquariums. If that isn’t an option, many bacteria additives exist on the market. We have had great success using bacteria additives. We specifically use Seachem Stability.

Once the beneficial bacteria is added, all we have to do is provide our friendly bacteria with a food source. There are two methods to achieve this, frequently referred to as ‘fish in’ and ‘fishless cycling’. For a fish in cycle, people generally add a single hardy fish to their new tank to produce small manageable amounts of ammonia. This provides sufficient food (ammonia) for the bacteria colonies to begin to propagate. If you choose this method, water parameters (specifically ammonia and nitrite) will need to be frequently monitored for the safety of the fish. Spikes in either ammonia and nitrite levels will require a large water change on the aquarium. The other, more fish friendly, method is a fishless cycle. In this instance, pure ammonia is added to the tank as a food resource for bacteria. If you decide to follow this method, make sure you purchase ammonia without any added detergents. ​

After we have initiated the cycle; we will need to monitor our levels of ammonia, nitrite, and nitrate within the aquarium water to insure the nitrogen cycle is taking place. You can anticipate witnessing a rise in ammonia first, with nitrite and nitrate level readings of 0. As the bacteria which consume ammonia (a.k.a. Nitrosomonas) buildup , you can expect to see ammonia levels fall and nitrite levels increase. As more nitrite becomes readily available, the bacteria known as Nitrobacter will begin to thrive. Nitrobacter will convert the nitrite in your tank into nitrate. You will know your tank is completely cycled when your ammonia and nitrite levels read 0 and you begin to witness nitrate levels within your aquarium. At this point it will be safe to introduce more fish.

Unfortunately, the name of the game is patience when it comes to completing a tank cycling. How long your cycling takes depends on several factors including the size of the aquarium and method of cycling utilized. We have witnessed cycles take only a few weeks and as long as a month or more. Even after your aquarium is cycled, increase your fish numbers slowly. Adding excessive amounts of fish at one time can cause an ammonia spike as the bacteria struggle to keep up. Just remember to be patient and frequently monitor your ammonia, nitrite, and nitrate levels in newly established aquariums.

That's it for this time. Until next time, Keep Krill'in!