Cycling A Freshwater Aquarium
Here's a common scenario: Someone buys a new tank and goes out the next day and buys fish. They die within weeks and the person assumes they just "aren't good with fish" and gives up.
It doesn't have to be that way. The reason those fish probably died was because of lack of bacteria. Yes, I meant to type that. The bacteria I'm talking about are the beneficial bacteria that keep our aquariums stable and safe for fish. I'm talking about the Nitrogen Cycle.
The Nitrogen Cycle
The problem is ammonia. Ammonia can be produced in many ways (the most common being through fish waste, un-eaten food, or dead plant matter). Ammonia is highly toxic and builds up quickly in a new aquarium. Remember that an aquarium is a closed system. All of these toxins stay inside the tank unlike nature where they are quickly broken down/eaten/carried away by currents.
Luckily for us aquarium keepers there are nitrifying bacteria that convert the ammonia into safer by-products. The first group of bacteria appear almost as soon as ammonia is present in the tank and they reproduce fairly quickly. They convert the ammonia into nitrite. Nitrite is also highly toxic so the tank isn't safe yet. After about a week a second group of bacteria will start to colonize and they will convert the nitrites into safer nitrates. A tank is considered "cycled" once ammonia and nitrite have stayed at 0ppm for a few days and nitrate is present.
Nitrates are fine in small amounts but if they build up they can weaken fish and sometimes even kill them. There are bacteria that can break them down but they don't do well in most aquariums so you can't rely on those. Instead you're going to need to remove the nitrates manually by doing water changes. A water change doesn't mean taking a cup and removing some water (except in some planted set-ups...more on that later).You'll need a gravel vacuum which can be bought at petstores for only a few dollars. It's a handy tool since it'll remove un-eaten food, decaying plant leaves, and fish waste while also removing a portion of the tank water. This means there will be less nitrates in the long run and they won't have a chance to build up.
The easiest way to start up a gravel vacuum is to submerge the whole thing in the water and let it fill up. Then place your finger over the small tube end and move it into a bucket. Remove your finger and if done correctly it should start the flow of water into the container. The power of the siphon will raise the gravel and will suck up wastes but not the gravel itself. In most aquariums you'll need to do at least a 20% water change every other week.
There are a few other ways to help keep nitrates down. Having hardy, fast-growing plants in your aquarium can help a lot since they will use some nitrates for food. Some commonly used plants are hornwort, water sprite, and java ferns. Another way is lightly stocking your aquarium...less food and less waste means less nitrates
. The third is by having nitrate-reducing filter media in your filter (but never rely on products like these too much...nothing is better then an actual water change).
So, how do you cycle an aquarium without fish? It's actually pretty simple. Since you don't have fish producing ammonia you'll need another source. Common ones are pure ammonia, fish food, and raw shrimp (this one might be pretty smelly but it's supposed to work well). You just add small amounts every day or two and test the water to monitor the water parameters. The tank is safe once there aren't any ammonia or nitrites. This usually takes about three or four weeks but it really varies. The only way to tell is testing the water. Don't worry if it seems like the nitrites are taking forever to go down. That's normal...usually they'll just suddenly drop after you start to give up hope.
Now that the tank is cycled, congrats! You can add fish
. But make sure not to add too many at once...the bacteria won't be able to keep up and the cycle will "crash". If that happens you'll see ammonia and/or nitrite spikes and an immdediate water change is required.
A few things not to do while cycling an aquarium are messing with the pH (it can harm the bacteria), changing the filter media or gravel (that's where the majority of the bacteria live), or performing too many water changes (you'll end up removing so much ammonia that the nitrifiers will die off). Also keep in mind that the bacteria need oxygen so make sure you have live plants or something moving the water (a filter, air stone, powerhead, etc.).
You might be wondering how you can speed up the cycling process. One way is to have live plants since they'll help out by absorbing ammonia/nitrites. You can also "seed" your tank with beneficial bacteria from a tank that's already cycled. The best way to do this is to take some filter media from that tank and place it in the filter or under the gravel of the new tank. Using gravel and water from a mature tank helps too. There is also a great product called Tetra SafeStart (formally known as BioSpira) which literally contains live nitrifying bacteria. It needs to be kept refrigerated so you might not see it right away even if they do sell it nearby. All you do is shake the pouch and then pour it into the filter (or over the bio-wheel, if the filter has one) at the same time you add the fish. I've personally used it three times and I never got ammonia/nitrite spikes...it actually cycled overnight. Avoid look-alike products...Tetra SafeStart is the only one proven to actually speed up cycling. Also remember to test the water often even if you used Tetra SafeStart since there have been cases of people receiving an expired pouch and having dead bacteria in it.
Even after your tank is cycled you'll still want to test at least once a week. You can get away with doing it less when your tank has been stable for a few months but don't forget the tests completely! Don't bother with the test strips as they tend to be inaccurate...go for the actual drip tests.
Earlier I mentioned how you wouldn't have to do many water changes or vacuum the gravel in some planted tanks. This is called a Walstad set-up (named after Diana Walstad who came up with the idea). There are many variations now but the concept remains the same...having a "natural" aquarium with little or no chemicals and lots of live plants. The idea is the plants will use the ammonia produced by fish as food and the bacteria aren't really needed. These aquariums are lightly stocked, well-lit, and heavily planted. Very few water changes are usually required but you will of course have to maintain the plants. You shouldn't vacuum the gravel either since it'll bother the plants' roots. Many Walstad tanks don't even have filters! I don't always recommend this but it can be handy when keeping fish like bettas who hate strong currents. I'll post some links on Walstad aquariums in case anyone is interested.
That's in case you didn't read everything :p.
Some Helpful Links:
Tropical Fish - New Tank (aquarium) Syndrome and Cycling
TFH's The Planted Tank - "Welcome to the Jungle"
"Ecology Of The Planted Aquarium" by Diana Walstad
(for those interested in planted aquariums)