Information on How to Cycle a Home Aquarium

All aquariums have got to be cycled before you put fish in them. It doesn't matter whether the aquarium is 5 gallons, or 500 gallons, it will not be able to sustain life without a filtration system that can process the toxic waste and remove it properly. Many people will probably cycle an aquarium without even realising it believe it or not. The first tank I ever got had small community fish in it, tetras and guppies. I couldn't understand why they kept dying, each day one of the fish would be floating on the surface, I kept replacing them each time one would die. After a month or so they stopped dying. What I didn't realise at the time is that I inadvertently cycled the aquarium. The small fish that I kept buying were providing the necessary ammonia that is needed to cycle an aquarium. The following article will explain how you can cycle your aquarium properly without losing lots of fish.

The nitrogen cycle

The image above shows how the nitrogen cycle works. You can see that ammonia is produced through the fishes waste and respiration. The ammonia is then converted to nitrite in your filtration system. A similar process using slightly different bacteria converts nitrite into nitrate. It's important to remember that decaying plants, food and any dead fish will also produce ammonia which will be processed in exactly the same way.

What Is Cycling?

Cycling a fish tank DOES NOT mean filling it with water and leaving it to stand for a week or two. it's very important that you know how to cycle a fish tank properly. 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 the term "cycling a fish tank" simply means establishing a bacteria colony in your filter so that fish will stay healthy and not die from toxic poisoning.


Freshwater Testing Kit

API freshwaterIn order for you to cycle your aquarium properly you will need to test the water on a daily basis using a special water testing kit. You can buy the individual solutions separately. However since you will be testing for ammonia, nitrite, nitrates and pH, you're probably better off buying a master test kit which comprises of all the necessary solutions you need. These test kits also come with four glass test tubes, easy to read colour chart and instructions. I have used API products for many years and in my opinion you cannot get a better quality water testing product. 

 I have found that eBay is about the cheapest place to buy water testing kits, there are plenty available for you to choose from


Cycling a Fish Tank

Traditionally there are two ways to cycle a fish tank. The most common way is to use fish as a source of your ammonia. The other way is to carry out a "fishless cycle". As the name suggests you don't use fish as a source of ammonia, you use liquid ammonia which can be found in household cleaning products.

If you are changing aquariums then you can use existing biological media from the filter that is running on the old tank, this biological media will already have healthy bacteria living on it. Obviously it very much depends on how much media you have at your disposal, but even a small amount will be enough to jumpstart the new filtration system. When we take existing media from an old filter to add to a new, we call this "seedling" the new filter. Just remember to keep the old media wet while you are changing aquariums. If the process of changing aquariums is going to take a while then you could help your beneficial bacteria by placing an air stone in with the media, this will oxygenate the bacteria and help keep them alive and healthy. If you are starting from scratch with a completely new aquarium filtration system then the whole process of cycling will take several weeks to complete if you are using fish as a source of ammonia. Cycling your tank using liquid ammonia can cut this period down considerably to just two or three weeks.

Some people like to use existing tank water, substrate, rocks and decor to help seed the new tank. Even though there won't be an enormous amount of bacteria present in the water and substrate, there will be some and every little bit counts.

You can use any freshwater tropical fish you like to cycle and aquarium, as long as you have a source of ammonia, the cycling process will be the same. However, you have got to remember that during the cycling process, the fish will be put under a lot of stress due to the amount of ammonia they will be exposed to. Therefore do not use Oscars to cycle your aquarium as you could damage their immune system. Even though they may survive the cycling, they could start running into health problems later on in life. It sounds a little bit mercenary but you are better off using fish that you are not going to keep long-term. You can use such fish as Danios, Barbs, Tetras, Guppies, Convicts, Plecos, Mollies, Firemouths. These are just a few that I know our members have used successfully. However, everybody will tell you that if you can get hold of some pre-seeded media then you will definitely aid the cycling process. Just be aware that you will be exposing these fish to high levels of ammonia so don't get too upset if you do have a few fatalities. I better mention goldfish while we are talking about what fish to use for cycling. There is a little bit of controversy to whether or not goldfish should be used to cycle a tropical aquarium. Some people suggest that because they are cold water they shouldn't be used. Other people are worried that because goldfish are produced in massive numbers, they can often harvest disease which can be passed onto your new aquarium. Having said this, some of our members have successfully cycled their tank using goldfish so that is something for you to consider. All I would say is that if you are going to use goldfish, source them from a reputable shop that can guarantee they are disease-free and healthy.

One important thing to remember is you will need some water quality testing kits that you will need to use every couple of days during the cycling process. Either this or get your local fish store to test your water for you. My advice would be to learn how to test the water yourself, it's very easy and isn't complicated at all. Knowing how to test your aquarium water yourself is really very important if you are serious about keeping tropical fish, especially Oscar fish.

If you are cycling a large aquarium then you may find it takes a day or two, maybe longer before the ammonia rises to a level that water changes need to be carried out. To be perfectly honest with you, it's very difficult for me to predict exactly when the ammonia in your particular tank rises to a level that the water will need to be changed.

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 so don't worry yourself if the ammonia remains present for a while. At some stage you will test your water and the ammonia will be 0. Then if everything runs smoothly, you will notice an increase in your nitrite level. Once again, your nitrite will eventually drop down to 0. you will eventually start seeing a nitrate reading. It may be a case that nitrate becomes present at a much earlier stage, however concentrate on your ammonia and nitrite until they remain stable at zero.  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.

When your aquarium is showing signs of being fully cycled, i.e. ammonia and nitrite are reading 0, and you have a decent amount of nitrate being produced, you can then start adding your fish. One important thing to remember is that a newly cycled tank will not be completely stable. Don't be tempted to go out and buy a tank full of fish straightaway. Introduce fish gradually and let your biological filter catch up with the bio load that the fish produce. You're much better off doing it gradually than risking running into problems by adding too much too quickly.

Cycling an aquarium can be both lengthy and frustrating at the best of times. If you are doing it for the first time then you may well be pulling your hair out after the first two or three weeks. The best advice I can give you is just stick with it and follow our instructions, eventually all will come good, I guarantee it :-)

So to reiterate on what we have learned:

  • You must cycle your aquarium before fish can live in it and survive long-term
  • You can either use community fish, or pure ammonia from a bottle to cycle your aquarium
  • If possible use biological filter media, gravel and water from a cycled tank. 
  • Test your water every day so as to maintain a safe ammonia/nitrite level 
  • Add fish gradually once your tank is cycled to avoid excess ammonia building up

cycling an aquarium-Tiger Barbcycle an aquarium with Mollycycle aquarium with convicts fishcycle aquarium with fire mouthcycle aquarium with giant Daniocycle aquarium with Tetracycle aquarium with guppy fishcycle aquarium with pleco

Pictured above are several fish that make good candidates for cycling an aquarium. Pictured from top left to right:

Tiger Barb, Molly, Convict Cichlid, Firemouth, Giant Danio, Neon Tetra, Guppy, Common Plecostomus


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/Bacteria Booster

You may have heard of "bacteria in a bottle" or maybe "bacteria boosters". These are products that come in the form of plastic bottles. The makers claim that live bacteria is contained inside these bottles. This live bacteria can then enable you to dramatically reduce the time it takes to cycle your aquarium. In fact Seachem Stability claim that you can add fish to a new aquarium straightaway if you are using their products. You may ask how the bacteria stays alive? Bacteria needs food, but it also needs oxygen. Apparently the makers add oxygen and food to the bottles which keeps the bacteria alive. You may then ask another question, what happens when the food and oxygen runs out? After all, some of this stuff has a shelflife of four years. Let's say that all the bacteria dies but the bottle stays sitting on the shelf waiting for someone to buy it. You come along, buy the bottle and then unsuspectingly pour a bottle full of dead bacteria into your aquarium, not really the best start in your aquarium life. Do I know this happens, of course not, but I can't think of any other scenario of what will happen to bacteria when they run out of food and oxygen.

It's been suggested by the doctor who discovered the two species of nitrifying bacteria in aquariums that it was actually the liquid food in the bottles that was shortening the cycle process, not anything to do with the live bacteria. The liquid food was actually acting as a food source for the newly forming bacteria in the aquarium.

Any of these products that claim to dramatically reduce the time it takes to cycle an aquarium, or tells you that you can add fish straightaway to a new aquarium should be viewed with scepticism. An aquarium is only fully cycle when the biological media in your filter is completely colonised by bacteria. Our advice on Oscar fish lover is to save your money and don't bother with any of these products. Cycle your aquarium the traditional way using either fish, or the fishless cycle, this way you know you will be doing it properly. 

I mentioned Seachem Stability as an example. It's only fair to state that other products they manufacture are extremely good and I use them myself.


Cycling without Fish

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 having to use fish. 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.