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Nitrogen Cycle

Besides the measurement of pH, the Nitrogen Cycle is the only other thing having to do with an aquarium that you need to take measurements on. It is very important, so please bear with us.
The Nitrogen Cycle is very simple, but it is VERY important – that’s why whenever we talk about it we capitalize the “N” and the “C”. The Nitrogen Cycle is what drives life on this little planet of ours, and in the case of an aquarium it is what makes it possible for fish to live in an incredibly small amount of water (compared to where they came from). The Nitrogen Cycle is what breaks down the fish wastes, so they can live in the confines of an aquarium. It works because of some different “good” bacteria that live in the tank. With the gravel, plants and the filter you are providing places for these bacteria to live. Fish wastes provide the bacteria with the food they need. It takes time (usually around 4 – 6 weeks) for the Nitrogen Cycle to become established during which time your water needs to be monitored regularly so you know what is going on.

Here’s how the Nitrogen Cycle works:

Fish are making waste products all the time; these products are basically ammonia. Decaying things in the tank, and excess fish food, also break down into ammonia. Ammonia is a deadly poison to fish – but thanks to the magic of the Nitrogen Cycle we have a way to deal with this. Some “good” bacteria convert the ammonia into nitrite. Nitrite is also dangerous for fish, not quite as bad as ammonia, but close. There is a group of “good” bacteria that convert ammonia into nitrite—the ammonia is the food for these bacteria. Fortunately, the Nitrogen Cycle doesn’t stop there. There is another group of “good” bacteria that convert nitrite into nitrate, which is not nearly as bad for fish as either nitrite or ammonia. Also, nitrate can be removed from the aquarium by live plants, which use it as their food, and simply by doing regular weekly water changes.

With your test kit/strip that measures ammonia, nitrite and nitrate you can measure the values for these three factors, plus the pH, and record it in your log book as you get the Nitrogen Cycle going in your tank.

“Cycling” a tank – Getting it ready for fish

You can’t just add a bunch of fish to your new tank and expect everything to be fine. As time progresses in your tank, the readings for these three factors, as you record them, will look like this if you put them on a chart – exact numbers and the curve of the graph will vary – it’s the basic process that is important to understand.

Here’s what you need to do, and what happens in your aquarium. Lengths of time are approximate – it’s the process that is important.

Week 1 – after your tank has been set up with water for two days, using water conditioner and the biological starter, you can add a few fish – 2 medium sized fish per every ten gallons. Choose hardy fish that you like, as they will be in the aquarium when the cycling is finished – We will help you on this, as with everything. Feed the fish very lightly every day. Take the readings for ammonia and nitrite every day or every other day, and record them in your log book. The ammonia should rise to a peak, and then start coming down. As it does the nitrite reading should begin to rise.

Week 2 – continue feeding, and do a 1/3 water change.

Weeks 3 -- 4 – by now the nitrite should be starting to come down, and the nitrate should be starting to build. When the nitrite starts coming down you can add some more fish – 2 more fish per 10 gallons as before.

Weeks 5 -- 6 – when the nitrite has gone down to zero and the nitrate is building, do another 1/3 water change. Now you can begin to add the rest of the fish to the tank – but a few days after you add new fish you need to check on the ammonia, nitrite and nitrate to make sure that the Nitrogen Cycle is in balance – that the bacteria have multiplied sufficiently to take care of the extra wastes produced by the added fish load.

The exact timing of establishing the Nitrogen Cycle will vary – it is the sequence that is important, and that you end up with zero ammonia and zero nitrite. Nitrate should be kept as low as possible (maximum of 30 ppm), which can be done through regular water changes. It is a good idea to test the tank water once a week for ammonia, nitrite and nitrate. If you have any problems with your fish, in order for us to help you out we need to know the numbers for ammonia, nitrite, and nitrate, and also for pH.

During the whole process of cycling a tank you need to observe the fish for any signs of distress, and make sure the water does not get cloudy. If the water is simply cloudy you are feeding too much – cut down how much food you are giving them. If the water is cloudy green you have an algae problem – cut down on the hours that the light is on every day, and on the amount of food you are giving your fish. Adding live plants will help immensely with any algae problems. Also, if you can get some gravel or filter media from an established, healthy, existing tank, putting that into your new tank will help things along. We do offer some “biological starters”, which are the bacteria that do the work in the Nitrogen Cycle. With these starter bacteria you can speed up the process, but you are best off by letting the cycle establish itself over a month to six weeks, as you slowly add new fish to the tank.