How to Cycle a Fish Tank

Always cycle your tank before adding Oscars

I thought it would be a good idea to briefly talk about "Cycling a Fish Tank". Now, if you search the Internet, you will find so many different ways of cycling a tank, it could become very confusing. Many people do it in different ways but at the end of the day, they normally end up with a properly cycled tank. If like most people you only plan on having one tank, this is a procedure that you should really only have to do once, unless you have a disaster at some stage. This is just the way I do it.

What Is Cycling?

Keeping fish in a fish tank is a huge compromise compared to what their life would be in the wild. Most fish that we keep live in literally millions and millions of gallons of water, they don't have to worry about ammonia or nitrite. However, once you put a fish in a small amount of water, the whole situation changes dramatically. If you don't do things properly, you'll poison the fish to death.

What you are trying to do is create a mini environment for the fish to live in. Obviously it is never going to be as good as in the wild, but you have to strive to make it as safe and liveable as possible.

Before you add any fish to a tank, it is vitally important that you prepare it properly so that the fish have a suitable environment to live in. It is not just a case of filling a tank full of water and plonking your fish in it. People who are new to fish keeping often go out and buy an aquarium set up, fill it with water and then just add their fish. They then start wondering why the fish start dying within the week. Basically, the fish are being poisoned to death by their own waste. A basic complete aquarium setup consists of the aquarium itself, a lighting system, a heater, and a filter. The heater and lighting are self-explanatory. However, the filter is a little bit more complex than a lot of people actually realise. Newcomers to Aquatics tend to think that the filter is just for removing debris from the tank. Yes, the filter does this, but that is only half of the story.

Your filter is actually the heart of your tank, without it, your fish will not survive. Whereas a brand new filter will remove solid waste, it will not remove dangerous toxins. The filtration system will only do this once you have the correct bacteria living within it. Growing bacteria in a new filtration system is commonly known as "cycling".

When the fish goes to the toilet, ammonia is produced (NH3, NH4). In a tank that has been cycle properly, the nitrifying bacteria that inhabit the filtration system turns ammonia into nitrite (NO2) which is then turned into nitrate (NO3).

So basically, cycling a fish tank means establishing a biological filter (i.e. cultivating a bacteria colony)

Cycling a Fish Tank

There are two ways that you can cycle a fish tank. You can either do it using fish, or do a fishless cycle. Seedling your tank at the very beginning is always a good idea. What this means is you add bacteria to the aquarium. There are various ways you can do this.

Use gravel/water or both from an existing cycled tank

Using filter media from a cycled tank (squeeze sponges out into your new filters or if you are using external filters with ceramic media, pour water out of the trays into the new filter. If there are any little bits of debris, put that in as well.

If you are not intending to use the old existing media then you could incorporate it in with the new media. Some people cut sponges up and add it into the new media. If you are using ceramic media, you could mix it in with the new media

During the cycling process you will need to test the water. You can either do this yourself, or get your fish shop to do it, they normally do it for free, or for a very small for charge. It is actually very easy to do it yourself, it is just a case of putting a few drops of a special chemical into a vile containing some tank water and then waiting for a few minutes to see what happens.

Once your tank is full of water, treat it to get rid of the chlorine. Chlorine and the beneficial bacteria in a fish tank don't mix. Chlorine will kill bacteria very quickly so beware. Go and get yourself a few community fish. Tetras, barbs and even guppies are good for cycling a tank. They are all cheap so it's not exactly a case of losing expensive fish if one of them does die, which will be a distinct possibility since they will be exposed to less than perfect water conditions.

Using your liquid test kits start testing the water maybe the day after you've added your fish. It's impossible to say how long it will take the ammonia to start rising. If you got very big tank and not very many fish, it may be a few days before your ammonia rises to the level where you need to carry a water change. On the other hand, if your tank is very small then the ammonia will probably build up a lot quicker.

If the ammonia is under 0.25 then you are okay. If it's between 0.25 & 0.5 then carry out a sizable water change, I would say nay more than 50%. If your ammonia is very high, 1.0 and above, carry out a very large water change, 75%, 80%. Many people do a water test directly after the water change. Sometimes you can get false readings doing it this way so always carry out your water tests before your water change. It's not worth panicking about, your water change should remove the ammonia so don't worry.

I'm not going to commit myself and say how long it will be before ammonia returns to zero, but at some stage this will happen, in the meantime, you will notice your nitrite getting higher, treat this exactly the same way as the ammonia. Finally, you will start seeing a nitrate reading. Nitrate is a byproduct of ammonia and nitrite and is not toxic. Once your ammonia and nitrite are zero, you have established a biological filter and your tank is cycled. The whole process could take six or seven weeks so be patient.

You often hear people talk of using very hardy fish to cycle a tank. I must emphasize that no matter what fish you use to cycle your aquarium, exposing them to high levels of toxins is not good for their health.

When you cycle a tropical aquarium using fish, you should use tropical fish. Danios, Tiger Barbs, Lemon Tetras are some fish I have used in the past. Many people use feeder goldfish to cycle a tropical aquarium. There are reasons why this isn't always a good idea. One of the main reasons is feeder goldfish are often mass-produced by breeders, they are often kept in very poor conditions which can lead to them developing disease and illness which if fed to your Oscar can lead to diseases or illness being transferred. So it makes sense not to use the same fish to cycle your aquarium where disease could be introduced. Goldfish are also cold water and require a different environment to tropical fish, optimum temperature for keeping goldfish is around 20°C. Keeping cold water fish in very warm conditions not only increases the chance of disease, but also increases the metabolic rate which means they eat all the time and produce enormous amounts of waste.

Don't be tempted to add too many fish straightaway, take it easy, you don't want to overload the system straightaway. If you do add too many fish, you could well overload the biological filter which could cause the tank to go into a mini cycle. This means that the ammonia and nitrite could suddenly be present once again. You would then have to go back to doing water changes every other day until the bacteria has got a chance to catch up.

API - Aquarium Pharmaceuticals

I have used various water testing kits over the years, Tetra and Hagan to name a couple. However, my favorite water tests are manufactured by a company called Aquarium Pharmaceuticals . I use their liquid water testing products such as the ammonia, nitrites, nitrate and pH tests. You can buy them individually or all of them together if you go for one of their master testing kits. The next best one in my opinion are manufactured by Tetra, although I have found these to be a little bit more expensive.

Bacteria In a bottle

There are various products on the market that supposedly contain the bacteria that remove harmful toxins such as ammonia and nitrite. They claim that when you add these products to an uncycled aquarium, they instantly establish biological activity to the filter. I now quote a company that sells these products "Enables rapid stocking of new aquariums by instantly establishing the biological filter" you'll noticed it says establishing the biological filter. The nitrifying bacteria that is present in your filtration system requires oxygen to stay alive. They also need a surface to cling to, so to speak. They are not free swimming like some types of bacteria. So if they are not the type of bacteria that are free swimming, and they need a surface area to cling to, i.e. your media whether it be sponges or little ceramic balls, how do they stay alive inside the bottle, or, have they used another bacteria? There are other bacteria that are present in a fish tank. These bacteria do break down such things as food, plant debris and dead fish. However, they are not the same bacteria that you find in your filtration system. So, if they haven't used the nitrifying bacteria in the bottles, how can it establish a bacteria colony in your filtration system?

Having said all this, this stuff does work. I haven't used it on a large aquarium with Oscars, only on a 20 gallon community tank with a few cory catfish. I set the aquarium up and introduced two Cory catfish. I then followed the instructions on the stress zyme bottle, add 10 mills to every 10 US gallons. That worked out slightly less in the UK. I had to do this on the 1st, 7th and 14th day. Intermittent water tests showed excellent results of no toxins present. Approximately 5 weeks after setting the aquarium up, I carried out a water test, ammonia, nitrite and nitrate. Ammonia and nitrite 0, nitrate in between zero and five. So, we have to conclude that this product does work because I have done no water changes since setting the tank up and I have had no ammonia or nitrite readings at all. And we have nitrate reading which means that ammonia and nitrite are being dealt with by the bacteria. I don't think you should let it go to your head, the bacteria colony will be newly established and will not be able to handle a large bio straight off. Add fish gradually and keep testing the water.

As mentioned at the beginning of this page, you can always do a fishless cycle. A fishless cycle is exactly how it sounds. You cycle the tank without fish. What you do is use pure ammonia. This is often found in hardware stores. Having said that, it isn't always easy to come by so you may have to look around. A fishless cycle is a lot easier and more convenient than cycling the tank with fish. For a start, you don't have to do any water changes and more importantly, there aren't any fish that are put at risk from high stress levels that would be caused by poor water conditions. For a more comprehensive look at a fishless cycle, visit this website

How to do a Fishless Cycle...