How to Cycle a Fish Tank
Cycling an aquarium isn't quite as complicated as you may think. In fact when many of us started out keeping fish, we inadvertently cycled our aquariums without even realising what we were doing. When I first got into fish I didn't have the luxury of the Internet where I could with the click of a button and the press of a few keys find all the information I needed. I started out keeping fish like guppies and other small community fish. I couldn't understand why all my fish kept dying for the first month or two, I would just keep replacing them as they turned belly up. Then after a few weeks they miraculously stopped dying, I had in fact inadvertently successfully cycled my aquarium without even realising what I was doing. Obviously for the sake of the fish and your pocket, you really want to try and avoid killing every fish you put in the tank during the cycling process. Thankfully we now have the Internet so there really isn't any excuse not to do it properly. This page will explain in basic terms what cycling means and how you go about doing it.
What Is Cycling?
Keeping fish in a fish tank is a huge compromise compared to what their life would be in the wild. Fish don't have to worry about ammonia or nitrite in their natural environment, they have millions and millions of gallons of water at their disposal. Once you put a fish into an aquarium you have a completely different ball game altogether, you now have a situation where dangerous toxins can easily overcome an aquarium and kill all of your precious fish. An aquarium that is properly maintained becomes a living environment that can sustain life for many years if maintained properly.
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 several community fish that produce the ammonia, or do a fishless cycle which involves using pure ammonia which can be purchased in bottles.
If you already have an aquarium setup and running then it would be very helpful to use either all, or if you intend on keeping that aquarium running, some of the existing media to help jumpstart your new filtration system. When we take existing media from a well-established filtration system to jumpstart a new filter, we refer to this as "Seedling". Introducing healthy bacteria to a new filter can often cut the cycling process in the half, obviously depending on how much of the old media you use.
If you are setting up a completely new aquarium from scratch and don't have any media from an old filter to add then the process will take several weeks to complete.
So to reiterate on what we have already learned:
If possible use filter media from a cycled tank. If using ceramic noodle type media, take a liberal handful and place them in amongst the new media in the new filter. If you are using sponge filtration, you can cut small chunks off the old existing media and place it among the new sponge media.
If you are closing down the old aquarium then use all of the existing media. This in theory well give you an instant cycle, obviously depending on how large the new aquarium is & how many fish you intend on putting it.
Use gravel/water or both from an existing cycled tank. This won't contain an enormous amounts of bacteria, but every little bit counts.
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 no 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 like ammonia or nitrite. 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. Try not to panic during the cycling process if one day your ammonia is higher than the previous day, if you just carry on monitoring the ammonia and nitrite and do water changes accordingly, eventually the bacteria in your filtration will buildup to the extent that you will not have any ammonia or nitrite present, but you have to remember it will take several weeks if you are just using a few small community fish, so be patient. Do not clean your filters during the cycling process, unless you have some very fine polishing pads that get clogged up very quickly.
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