Cycling an Aquarium

The nitrogen cycle is criticle to maintaining a healthy aquarium.

by fballguy


Ok so you just got your new tank! Congratulations! Now all you have to do is wait the 24 hours the employee and the local fish store said to do. Right?


The nitrogen cycle is critical to maintaining a healthy aquarium. Here is a short summary of how it works:

Fish, rotting food, plants, ect. all produce toxic ammonia. Ammonia will kill fish even in very small amounts. Fortunatly there is a solution to getting rid of ammonia. You guessed it, the nitrogen cycle. Nitrifying bacteria lives in your filter, on gravel, decor, ect. Most of it will be in the filter. This nitrifying bacteria consumes toxic ammonia and converts it to nitrites. These nitrites are also very toxic, and will kill fish in very small amounts. I know what you are thinking. What is the point of this bacteria if all it does is convert poison to another poison? Well, that's where a different kind of nitrifying bacteria comes in. This bacteria converts toxic nitrites to the much less toxic nitrates. In nature, the cycle continues from there, but in the aquarium, this is almost impossible to achieve. For this reason, water changes must be performed to remove nitrates. Nitrates are not all that toxic, but they will still harm fish if water changes are not performed to remove them.

So now you ask, how do I get this cycle started? Well, once you get the tank all set up, with filters running, it is time to get starting cycling the tank. There are a couple of ways to get it going. First I will go over the way most fishkeepers reccommend. For all methods, you are going to need a test kit that tests for ammonia, nitrite, and nitrate. Try to avoid test strips, they are unreliable and innacurate. Liquid tests are much better.

Fishless Cycling:

For this method, you will be providing the tank with a source of ammonia. Bottles of ammonia can be purchased at your local department store or hardware store. Make sure to get pure ammonia, some of it has chemicals added which are harmful and will kill anything living in the tank. Read the ingredients label to make sure there are no additives.

Add the ammonia to the tank slowly, and check the levels every little bit of ammonia you add, repeat until the ammonia level is at 5ppm. Do not let it go above 8 ppm, if it does get that high, change out some water to bring the level back to around 5ppm. Test ammonia levels once every 1-2 days, and add ammonia as needed to keep the levels at 5ppm. Within 1-3 weeks, ammonia levels will start to drop, and nitrites will start to appear. Once nitrites appear, keep adding ammonia, but this time only go up to 2-3 ppm ammonia. Ammonia will slowly fall as nitrite levels climb. Test for both ammonia and nitrites every day. Nitrites will probably climb off the charts. Just let them go, and in 1-2 weeks nitrites will dissapear and you will start to see nitrates. When nitrites hit zero, dose 5ppm ammonia and wait for 1 day. By the next day there should be 0 ammonia, and 0 nitrites. Test for nitrates, and change water as needed to bring nitrates down to 10-20 ppm. It is now time to add your fish!

Cycling with Fish

 This method is not reccommended, because it can cause damage or death to the fish, but many people go out and buy fish before finding our about the cycle, and fishy cycling has to be done. For this method, again, have the tank, filters, everything set up. Add a small load of fish, make sure the fish are a very hardy type, because the ammonia and nitrite levels are going to have an effect. Monitor ammonia and nitrite levels very closely, and change water often to keep those levels as close to 0 as possible. If they rise above 0.25 ppm, do a water change. Once ammonia and nitrite levels hit 0, and nitrates start to show, it is time to add your fish. Gradually add fish, 1-2 small fish per week, and continue to monitor levels very closely. The bacteria will increase gradually with each fish you add, as it will need to adjust to the higher bio-load. So make sure to add fish gradually, and be patient.

Cycling with Established Bacteria

This is the easiest and fastest way to cycle an aquarium. There are different ways to get bacteria for your tank. The cheapest way is to get some from another tank. Get some filter media from a friend, or maybe even your local fish store, and put it into your filter. Add a small load of fish, and monitor levels. Change water if needed to keep ammonia, nitrite as close to 0 as possible. In about a week, levels should hit 0, nitrates will begin to climb, and you can add 1-2 more small fish. Repeat until desired stocking is achieved.

You can also buy bacteria from the store. Don't trust anything that is off the shelf. These products are all live bacteria, and sitting on a shelf will cause the bacteria to die, and you will waste your money. Instead, go for products that are refridgerated. This causes the bacteria to go dormant, and they will live much longer. I reccommend Marineland's Bio Spira, it is the only product that has had widespread success. Follow the instructions on the package for use.



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