Friday, April 29, 2011

Fish Care: The Nitrogen Cycle

For new fish keepers the nitrogen cycle can be intimidating. It can seem quite complicated and confusing, but it is actually pretty simple. It all has to do with bacteria and your fish's waste.


Fish produce waste. This fish waste produces ammonia. Ammonia is toxic to fish if the levels are too high. So good bacteria breaks down the ammonia into less toxic nitrite. However nitrites are still toxic to fish at high levels, so bacteria will break down nitrites into even less toxic nitrates, which plants use for nutrients.

That is the nitrogen cycle for fish. 

Now in the wild, fish live in what is called an "open" system. Basically, when the water becomes unsafe, they can flee to safer waters. But, in an aquarium/fish tank, the fish live in what is called a "closed" system, meaning they cannot flee when the water becomes unsafe for the fish.

Therefore it is a fish keeper's responsibility to monitor the nitrogen cycle. A fish keeper needs to regularly test the water (weekly is recommended), to make sure the levels of ammonia, nitrite, and nitrate are at safe levels and won't harm the fish. This can be done either using test strips for fish tanks or a liquid test kit.

Another responsibility of a fish keeper is to start the cycle. In a new tank, their won't be enough bacteria to successfully convert ammonia into nitrites and nitrites into nitrates. The cycle can't start by itself in a closed system. Not starting the cycle in a fish tank is the leading cause of deaths of new pet fish. 

So here is what to do: You need to start the bacteria, which can be done in a number of ways. Basically you need to feed the bacteria.

Sometimes fish keepers put hardy fish such as danios, tetras, and sometimes barbs, into the fish tank first. The waste from these fish will encourage the bacteria to start. However, I do not recommend doing this for a few reasons: it is extremely stressful to these fish because the bacteria will not have built up enough to eliminate the fish's waste so ammonia levels will get pretty high. You also might not even want any of these fish, so this might not even be an option. There are easier ways that don't involve stressing out the fish.

You can use water from another (established)  tank in your new one, or gravel from an established tank. This is very easy, because the water or gravel will already have an established amount of bacteria, and the tank will be cycled pretty quick. The downside to this is that you need an already established and still running tank.

In my opinion the best way to cycle the tank, is to use bacteria supplements and fish food. You can buy a liquid bacteria supplement at the pet store for just a few dollars and this will feed the bacteria and encourage bacteria growth. To help, add a few fish flakes to the tank. The food will produce ammonia for the bacteria. You can also go to the grocery store and get a shrimp (a dead shrimp obviously) and put that into the tank. The bacteria will LOVE it.

Here's a tip: When you see a bottle of stuff at the pet store labeled "LIVE BACTERIA" it most likely is mostly dead. Bacteria need oxygen to survive so if it is has been in the bottle for a long time odds are a lot of that "live" bacteria is dead. However it is still good to add to the tank to encourage bacteria growth, just keep in mind it isn't really "live" bacteria, it is basically just a bacteria supplement.

Cycling a new tank takes a while. Cycle  it with bacteria supplements for at least a few days (for instance I am waiting at least five days before I add my betta fish (bettas are hardy fish) before adding fish. It is best to only add hardy fish at this time. They should be fine because there will be some bacteria in the tank by now. Just be sure to test the tank first and make sure the ammonia levels are at zero before adding the fish. And only start with one to three fish. This way the ammonia levels won't get to high. After about four weeks the cycling should be fully finished an you can add whatever fish you want. Save less hardy and more sensitive fish for when the cycling is done and the bacteria is fully established.

Just a note: Cycling the tank without fish by using bacteria supplements is usually quicker than cycling with fish and can take as little as two weeks. I forgot to mention but you can buy liquid ammonia from pet stores to cycle the tank with. 

1 comment:

  1. The only fish I had was a goldfish or two. We had the standard goldfish bowl with gravel, a little ceramic bridge to swim through and some sort of plant. Can't remember how often we cleaned it but we just put the fish with some of its water in a glass then scrubbed out the bowl, put in plain old tap water (which now that I think about it was probably chlorinated) and put the fish in. I guess goldfish are pretty hardy because they did live for quite awhile. It's great that you have so many things available to help care for your fish properly.
    Good posts!
    -Goldfish Granny