What is Aquarium Cycling? How to Cycle your Tank
What is aquarium cycling? It has been my unfortunate experience in my 7 years of fish keeping that the majority of casual fish keepers have no idea what the answer to this question is. This article hopes to explain what cycling is, how to do it and how to avoid accidentally killing your fish. It is not the most in depth explination, but I hope it gives you at least a general sense. At the very bottom I have included some very useful links.
Whenever I ask someone “Did you cycle your tank before adding fish?” most answer “Yes.” I always have to ask the follow up question “How did you cycle it?” to which I am always answered “Well, I let it sit for a day/a couple days/a week/a couple weeks.”
Cycling is not letting your tank sit for any amount of time before adding fish. Cycling is referring to the nitrogen cycle, which only takes place after fish or some source of ammonia is added to your tank.
The aquarium cycle can be confusing and daunting for any new aquarist. Water chemistry? Water tests? Bacteria and nitrates and stuff I don’t understand! Please, for the sake of your fish at least have a general understanding of cycling. It is the most important aspect of keeping fish in captivity and without it or an understanding of it it’s nearly impossible to keep fish alive and healthy for any substantial amount of time. Indeed, the leading cause of fish death is an improperly cycled and maintained tank. That’s right, whenever a fish dies it’s almost always your fault for improper care. It’s hard to hear, especially for newcomers, but it’s true.
So what is cycling?
Cycling is the build up of beneficial bacteria in porous surfaces in your aquarium (your sand or gravel bed, your filter pad/sponge, rocks, and even some in your water itself) which then breaks down toxic ammonia (NH3 or in low pH levels ammonium NH4+) into just as toxic nitrites (NO2-) and then into less toxic nitrates (NO3-). Nitrates eventually leave the aquarium in the form of nitrogen gas. These bacteria are gram negative anaerobic (preferring little or no oxygen) nitrobacter and nitrosoma.
Here is a visual aid:
(source)
The Process
The simple answer: You add fish or some other source of ammonia. Bacteria builds up in your filter pad and breaks that down into just as toxic nitrites, and then into less toxic nitrates. This can take anywhere from 6 weeks and up to happen, and it is important to test your water during this time. If you have fish in the aquarium, you must perform frequent water changes to keep your ammonia levels at 0. Contrary to popular belief this does not slow down or interrupt your cycle.
The long answer: Every organism had some nitrogen in it, it’s essential to all life. Every organism you add to your tank releases nitrogens. Plants, fish, live rock, corals, even food. This nitrogen (ammonia) is toxic to fish, snails, shrimp, and anything else really. Beneficial bacterial colonize (i.e “glue themselves to) things like the "media” in your filter. Sponges, filter floss, ceramic, and volcanic rock are all good surfaces for bacteria to colonize on but it also lives in your gravel and any other surface it can cling to.
This bacteria (nitrosoma) are autotrophic, which means they produce complex organic compounds from simple inorganic ones to produce energy. These bacteria need some oxygen and water flow to colonize, which is another reason why most of your bacteria is in your filter media. So after ammonia is introduced the nitrosoma break it down into nitrites which is when the nitrobacter come in and break that down into nitrates. These nitrates are then either absorbed by plants (later to be released in the form of dead leaves) or turned into gas and evaporate. Fresh water fish tolerate nitrates in a huge range. Some species are fine with 10ppm, and some as high as 40ppm. Saltwater fish are much more sensitive and nitrates should be kept close to 0 at all times.
Methods of Cycling
There are a few different methods of cycling. If you already have fish in an uncycled tank, please scroll down to that section immediately. A fishless cycle is the use of some ammonia source that is not a fish, thereby eliminating the danger of killing your fish by exposure to ammonia and nitrites. Popular sources include pure ammonia (free of fragrances, “surfacants”, dyes, etc.Shake the bottle. If it foams, it’s not safe.) seeding, and fish food (dry or frozen though it’s been my experience that frozen works better)
The ammonia method. This is probably the best method aside from seeding as it does not involve putting fish in harms way, using food which can attract saprolegnia (a fungus) and is relatively inexpensive. Add 3-5 drops of ammonia per US gallon of water until your ammonia is 4ppm. (scroll down for the section on water testing) Wait 20 minutes or so and test again, if needed raise the ammonia again. Continue this (Keeping your ammonia at 4ppm. Test it daily and add more ammonia if you need to!) and you will see your nitrites spike and fall, then your nitrates. Once you have nitrates of 40ppm or so you can perform one large (50-80% depending on your levels) water change and add fish!
The fish food method. This is by far the easiest and least expensive method that does not involve adding existing bacteria to the tank, but has the drawback of attracting mold and fungus. Rotting food is decomposed by saprolegnia, an infection which can spread to fish. “Feed” the tank daily, attaining an ammonia level of 4ppm just like with the previous method. Simply add more food and keep the ammonia there and cycle it just like the ammonia method. I have tried this personally with success. The only extra step is making sure you siphon out any and all rotten food.
Seeding. This is using used filter media from an establish (cycled) tank to jump-start your new tank. Use a sponge, filter floss, ceramic blocks, or volcanic rock and simply put them in your new tanks filter. Wait 1-2 days and slowly start introducing fish, while testing the water daily and performing any water changes as needed.
Bottled Products. Ok, more sorta complicated stuff ahead. Most bottled products do not contain nitrosoma and nitrobacter, but instead contain heterotrophic bacteria, which have a reasonable shelf life and much higher reproductive rate than true nitrifying bacteria which are autotrophic. Their drawback, however, is that they are not nearly as good as breaking down ammonia as true nitrifying bacteria so it takes much more of them to do the job. Many if not most of these products do not work. Either they do not contain the right kind of bacteria or it is dead.
The only products that work to my knowledge are; Biospira (Now Dr. Tim’s One and Only and Tetra Safestart), SeaChem Stability, and FritzZyme TurboStart 700. Keep in mind that heterotrophs cannot truly cycle an aquarium and should only be used as an aid to deal with ammonia spikes.
Fish-In Cycling
You have fish, you put them in a new tank, and suddenly you’re hearing all about this cycling stuff for the first time. What do you do? Go out and purchase a liquid test kit (API is the most commonly available brand) an aquarium siphon, and a 5 gallon bucket from a hardware store. These will be your tools. Without them, you may very well kill your fish.
“But I’ve always done it this way! I just get cheap hardy fish and add them to the tank first.” In this case, you’ve always done it the wrong way. Tell me, how many times have you lost fish this way? How long did your fish live AFTER this? Chances are you’ve been doing everything wrong and you haven’t kept any of your fish alive for their whole lifespan. Sure, things like guppies only live 3 years but many tetras live to be 7-8 and goldfish live to be 15-20!
Keep your filter and heater running like normal and test your water every day. As soon as you see any ammonia or nitrites, do at least a 25% water change. Make sure to siphon your gravel as well as remove water. Otherwise feces and food just sits there and rots. Always replace water with tap water that is close to the temperature of the tank and has been treated for chlorine/chloramines/heavy metals with some kind of water conditioner or RO (reverse osmosis) water. Continue this for at least 6 weeks, or until you have nitrates of 15-40ppm. Then you can do water changes at a regular rate. Which varies wildly depending on your tank size, which fish you have, how many you have, if you have live plants, how often you feed them, and what kind of filter you have.
Test Kits
Test kits are extremely important. Water can be crystal clear and deadly to fish! Dirty water does not mean cloudy water. Aquarium Pharmaceuticals Incorporated (API) sells a decent liquid test kit that is suitable for home use. However, it is never 100% accurate.
Never use test strips unless you are simply test pH. All other test strips are, in general, so inaccurate or likely to be compromised/damaged and not work they are a waste of money.
Sources
Here are some very VERY good reads that go a lot more in depth than I am able to. I highly recommend reading them, or at least the first one.
AmericanAquariumProducts article on cycling
AquariumAdvice’s forum thread with a great step-by-step guide
TropicalFishKeepers beginners guide to cycling
AquaticCommunity’s article on cycling
Wikipedias entry on the nitrogen cycle
FreshAquariums article on cycling
FishLores article on cycling
FishChannels article on cycling
