The Cycle of Life
Ok, you have come a long way. You started with nothing but the desire for a saltwater aquarium, and now you actually have one functioning right in front of you. I'm sure at this point you are anxious to run to the store and start buying fish and have your mini-ocean come to life. However, as with every aspect of this hobby, you must prove patient once again.
You have read bits of information before about "cycling your tank", but until now I have not really gotten into this subject. This is a process that must begin before you can begin inhabiting your tank. The "cycle", or more specifically the Nitrogen Cycle, deals with the Ammonia, Nitrite and Nitrate levels of you water, and a few different types of bacteria that become the workhorse for your biological filtration system. At all times during the life of your tank uneaten foods, decaying matter and waste products, from tank inhabitants, are broken down by bacteria. The resulting product from this process is Ammonia. Ammonia is extremely toxic to fish and must be removed immediately. Well, that is where the "ammonia loving" bacteria, Nitrosomonas, come into play. These bacteria will go to work on the Ammonia produced, and converts it into Nitrite. Nitrite is better than Ammonia, but not much. So, the Nitrite must also be broken down. So, you guessed it, another type of bacteria goes to work on the Nitrites. Nitrobacter turns Nitrite into Nitrate. Now, Nitrate is actually fairly harmless to fish. Some corals and plants do not tolerate very high nitrate levels, but for the most part are "safe". Of course, you still want to get rid of Nitrates. Systems that incorporate refugiums help to break down the Nitrates by keeping macro algae. Other systems that utilize a "de-nitrafier" then convert the Nitrates into Nitrogen. But don't worry about having a refugium or a "de-nitrafier" right now. In fact you may never get one, which is fine. Most people new to the hobby keep Nitrates in check by performing routine water changes.
So, you may be asking yourself, "If I don't have any waste in my system then why am I worried about it yet?" Well, you're right to wonder. In fact, if you do not have any waste at all, then why would the colonies of needed bacteria develop? They wouldn't. So, you have to introduce these bacteria and actually force your tank to cycle. If you don't, there will not be the required biological filtration needed to support the life you may add. For instance, if you went right out and purchased a few fish. After you add them they will begin to produce waste products. Uneaten foods and waste would begin to build up. The bacterium that breaks these products down would begin to develop. What would occur would be initially an Ammonia spike. Meaning the Ammonia levels would skyrocket to unhealthy levels because the Ammonia loving bacteria would not be established to break it down fast enough. The result would be the loss of many of you fish due to Ammonia poisoning. If any of them lived through it, they would then be exposed to a Nitrite spike once the Ammonia was broken down. The reason would be the same. The Nitrite loving bacteria would not be established enough to convert the Nitrite into Nitrate. You can see the pattern here.
Here is the bad news. Before you can begin stocking your tank, you need to let it completely cycle. This can take as long as a few weeks. Here is the good news. There are many ways to drop this time down to a couple of days. If you add live sand and live rock, you will be putting colonies of these beneficial bacteria directly into your system. The more live rock you can add the better. There will be some die off and decay as a result of introducing the rock to your system. Between the die off and bacteria, your system will begin its cycle. If you do not want to add any rock, then you can go with another method. You can take cut pieces of fresh shrimp and drop it into your tank. As the shrimp breaks down and decays, the bacteria will also begin to develop, hence beginning the cycle. Aside from those methods, concentrated bacteria has actually been bottled and sold recently just for this purpose. You can pour it directly into your system and instantly your tank has armies of bacteria ready to work.
Now there is one other method for accelerating your cycle time, but I disagree with it for a couple of reasons. This method is actually one of the most popular, and I'm sure your local fish store will suggest this to you. A lot of Damselfish are extremely hardy. So hardy, they can withstand the extreme spikes your aquarium goes through during its cycle. By adding the Damsels, they will produce waste and assist in the cycle process. Many people love this because it means that they can have some fish right away. However, I would like to at least touch on two issues before you do. First of all, a lot of the Damsels can become very aggressive and annoying pests to a tank as they mature. I agree they are very attractive, however you may learn that their territorial behavior inhibits the wellbeing of some of your more peaceful tank mates. You may think that you can just take them out when you want to, but you do not know the frustration of trying to catch a tiny fish in a large tank with tons of hiding places. So, don't just add fish without thinking it through. Don't get me wrong, there are a few Damsels that are relatively peaceful and make a great addition to your tank, but continue reading my next reason. The second point is even more important, at least to me. You have to think to yourself, just because this fish can survive through the Ammonia and Nitrite spikes does not mean it should be subjected to it. This is obviously a debatable topic, but the bottom line is the fish will be subjected to unhealthy conditions. I believe it to be a cruel process when there are so many other options. However, the choice is yours obviously.
No matter what methods or techniques you employ, you need to monitor the cycle. This is where that test kit I had you buy will start to earn its keep. This is great practice for the beginning aquarist anyways. You will always test for pH, Ammonia, Nitrite and Nitrate as long as you have your tank. During the cycle you will be able to witness the spikes mentioned earlier. Once you have seen the Ammonia spike, followed by the Nitrites and then the Nitrates you can consider your tank "cycled". However, to be sure, test your Ammonia and Nitrite levels, both should show zero in your tank. If it does not, allow your tank to cycle more. Now is the time you have been waiting for.