Owning a Saltwater Aquarium Part 3

(Part 3 in Life Aquatic’s Series of Owning a Saltwater Aquarium)

Cycling Your Marine Aquarium

Now that your tank is filled with water and the equipment is running, the next step begins which is cycling. “Cycling”, which is short for the Nitrogen Cycle, is the process by which beneficial bacteria begin to populate your filter media, rock, substrate and water. To start the cycle, a source of ammonia needs to be introduced into the tank. In an established aquarium Ammonia is produced by an animal’s respiration and waste and is also produced by the decay of things such as uneaten fish food. In a new tank, these things are not present so a catalyst needs to be introduced which will start the process. In the old days (and unfortunately, in some cases, still today) aquarium keepers used to add live fish into to the tank which would breathe, eat and produce waste. These functions would produce Ammonia which would start the cycling. Unfortunately, the fish may or may not have survived this process and even if they did survive, they were put through torture having to endure nearly toxic levels of ammonia and nitrite. Today, we realize that the same result can be achieved without sacrificing a living thing. Instead, all we need to do is introduce a food item which will naturally decay in the tank. We recommend going to your local supermarket and buying a few raw, uncooked shrimp or scallops and just throwing them in the tank. In short order they will begin to decay in your tank which will process ammonia and the cycle will begin.

Fully cycling a saltwater aquarium takes approximately 4-6 weeks. During this time beneficial bacteria start to form which begin breaking down the deadly ammonia produced by the above processes and convert it to slightly less toxic nitrite. Then a different type of bacteria form which begins to break down the nitrite into less toxic nitrate. Some of the nitrate naturally dissipates during gas exchange that takes place at the water’s surface, but for the most part, the only true way to get rid of nitrates is through regular, partial water changes. Marine animals can tolerate low amounts of Nitrate and just about every tank has measurable Nitrate present. The goal is to keep this level as low as possible which can be accomplished by changing some of the water.

Some animals are hardier than others and can withstand different levels of Nitrate and even some Nitrite. Accordingly, it is possible to add certain animals before the cycle has completely run its course. Before adding even the hardiest animals such as snails and crabs, your Ammonia level must be at zero. At this point you will have still toxic levels of Nitrite, but a few snails and hermit crabs can exist in this environment for a limited period of time. As time goes by a few more hardy animals can be introduced, one at a time. Throughout this process, make sure there is a continuous presence of decaying food in the bottom of your tank to keep the beneficial bacteria thriving. Once your tank is stocked, this won’t be necessary as the inhabitants will produce a never ending supply of ammonia through respiration, waste elimination and the decay of any uneaten food which may find its way into a nook or cranny where your animals can’t reach it. But by this time the different strains of bacteria will be present in sufficient numbers to handle the processing of these organic by-products. Partial water changes will complete the removal (or in the case of Nitrates, minimalization) of these substances.

So how do you know when your tank is fully cycled? Your tank is cycled when your water tests zero for Ammonia, zero for Nitrites and tests about 25ppm or less of Nitrate. At this point livestock can slowly be added to your system. Each time you add a new animal the population of beneficial bacteria will increase to levels necessary to process the amount of waste that is present. Never add many animals at the same time as the bacteria population will not be able to rise quick enough to handle the new bio-load. If your tank has only one existing fish and you add another, you are doubling your bio-load. If your tank has four fish and you add one you are only increasing the bio-load by 25% (assuming the same sized fish are being added). Use this as a guide in adding new livestock. Once you have a small handful of animals try not to increase your bio-load by anymore than 20-25% at a time. Also, keep in mind that all fish are not equal when it comes to producing waste. In general, it is the mass of the fish, not just the length that determines its organic contribution to the tank. A 4” fish for example, will produce 64 times the ammonia than will a 1” fish. The old rule of 1” of fish per gallon of water is fine if you’re talking about a 1” fish. While you can possibly put 64-1” fish in a 64 gallon tank, you can, in theory, only put in 1-4” fish. Go beyond that and you’ve reached the ultimate limit to the amount of bio-filtration that can exist in a given size tank. This is one of the main reasons you can’t just keep adding and adding livestock.

We mentioned early on in this discussion that there are some ways to speed up, but not eliminate, the nitrogen cycle. One way is by adding live sand and live rock to your system. Live sand is ocean sand that has been packed in water and already contains billions of beneficial bacteria. This will jump start the cycling process. Live rock is rock that has been continuously under water and also contains billions of beneficial bacteria (not to mention lots of other cool critters). By adding live sand and live rock to your system in the beginning, you can speed up the process of cycling and cut perhaps a few weeks from the normal 6 week waiting period. There are also bacterial cultures available which come in bottles and can simply be poured in the tank. Any of these methods or a combination of all three may be used to help speed up the natural process of aquarium cycling.

By the way, do not perform any water changes during cycling, though you should replace any evaporated water with fresh, non-salted water. Also, your lights can stay off during the entire cycling process, if you choose.