The simplest way to “cycle” an aquarium before adding fish is just to add half a teaspoon of fish food per twenty gallons once a day for six weeks. Do NOTHING in those six weeks, even if the tank gets gross. “Cycling” is the term used for growing colonies of something called “beneficial bacteria”. These bacteria convert toxic fish pee (ammonia) to a relatively innocuous compound called nitrate. Growing these colonies normally takes 4 to 6 weeks. These colonies are the brown gunk that forms on the filter media in the filter.
There are literally hundreds of ways to successfully “cycle” an aquarium. This makes any discussion of cycling a bit verbose and lengthy. What follows below are short synopses of the two most common methods: Fish-in cycling and Fishless cycling.
What is “Cycling”?
“Cycling” is the term used for growing colonies of something called “beneficial bacteria”. These bacteria convert toxic fish pee (ammonia) to a relatively innocuous compound called nitrate. This process is called the “nitrogen cycle”. These colonies are the brown gunk that forms on the filter media in the filter.
In a new aquarium being started up these “beneficial bacteria” take anywhere from 2 to 8 weeks to grow to sizable colonies. So, if you put fish in an aquarium right away, those fish may get very stressed from their pee and may, in extreme circumstances, even die. Note that one has to add a lot of fish to a new aquarium and feed them a lot to get conditions that harm the fish.
Most hobbyists start up a new aquarium by running it as a filtered heated aquarium with food being added daily for 4 to 8 weeks. This is called “cycling” an aquarium. Typically, this is best done with no fish in the aquarium. Easy.
Note that if a newcomer to the hobby goes up on social media and asks how to cycle they will get a huge number of conflicting answers. The reason for this is simple. There are hundreds of ways to cycle an aquarium. Indeed, if one doesn’t formally cycle an aquarium, Mother Nature will do it for you. Thus the confusion.
Directions for a Beginner
If you are a beginner with a new aquarium, keep things simple. Fill the aquarium with water and add chlorine conditioner per the directions. Start all the filters. Don’t add any fish or any plants. Aerate the water well with air stones and an air pump.
Add at least one level teaspoon per 25 gallons of brown gunk-filled material from an established aquarium filter (the best material), composted (WELL COMPOSTED, not fresh!) cow manure, or dirt from the garden, or the soil from a potted plant to the new aquarium. These “seed” materials all contain lots of beneficial bacteria which will jump-start the cycling process in the aquarium. Note commercial packaged potting soils are sterilized and will not work. Put the seed material in a sock (cloth sock for your foot) and put it in the filter. Squeeze the sock every few hours. Remove the sock after two weeks or so.
Aerate the water with an air stone and an air pump. Add about half a teaspoon of dry fish food per 100 liters of water per day. Continue to add the food daily until your tank is broken in. The food gets all dirty with white “stuff”. Ignore it. The food must decompose to feed the beneficial bacteria.
Just let the aquarium and the filter go for about four weeks with no water changes or filter cleanings. The tank may get very cloudy and even smell or turn green. Ignore it and just be patient. When the water clears or after at least four weeks of feeding your tank is ready to add fish. Easy!
Some want more control and want a “test kit” of fluids that test the levels of ammonia, nitrite, and nitrate in the aquarium water. If you want to head that way after about two weeks, buy an aquarium test kit and measure the ammonia and nitrite. Strip tests are fine as long as you get one that measures ammonia. This is OPTIONAL . It’s not a necessity.
Continue to measure every other day or so until the ammonia peaks and begins to fall. Continue to give ammonia or feed until the end of the cycle. Then start measuring the nitrate (note the difference between nitrate and nitrite) together with the ammonia and nitrite. In most cycles the nitrite then gets high and then starts to fall (sometimes nitrite never shows up!). And nitrate levels normally continue to rise throughout the cycle, from beginning to end. Note that the beneficial bacteria sometimes store the nitrates in their bodies so that protein and nitrate levels do not rise. So very rarely nitrate levels don’t rise.
If both the ammonia and the nitrite are at zero 24 hours after adding ammonia, feed or urine, the aquarium is turned on. At that point, if you have more than 80 ppm nitrate, you need to do a 50% water change. If you have 160 ppm nitrate, change 80% of the water. And then you have a ‘turned in’ aquarium. Simple!
Many newcomers get fish when they buy their aquarium. Luckily most folks start with something like “five little tetras of various types, a glofish, and two platies in a 20-gallon aquarium”. This is very light stocking and the fish will do decently well if fed lightly. One term for this is “fish-in cycling”. Many experts recommend this method of cycling a tank as the least complicated and easiest method for a beginner to understand and practice.
This is contrary to what all the naysayers say on social media but newsflash, fifty years ago no one did “cycling”. They just tossed the fish in. And if they didn’t stock too high or feed too much they were just fine! The fish lived long and “happy” lives.
Note that we don’t recommend fish-in cycling, fish-less cycling is the method we prefer and use. But it is extremely common for a newcomer to the hobby to find themselves with some fish in an aquarium that isn’t cycled. The newcomer must realize that they can do a fish-in cycle very easily with absolutely NO damage to their fish.
For simple “fish-in” cycling (cycling with fish in the aquarium) just feed the fish very lightly for the first few weeks. Don’t feed the fish for three days. Then feed the amount of two eyeballs (six fish = twelve eyeballs) every three days for two weeks, then every two days for two weeks, then everyday as regular feedings.
It is important not to thoroughly clean or change out the filter media or cartridge at this point. The beneficial bacteria colonies are in the gunk on the filter media and throwing them out or cleaning them out starts the cycling anew.
You may want to do more rigorous and complicated “fish-in cycling” of a tank. It isn’t critical to do this but it is the safest course of action for the fish. Click on this link:
2.5. Fish-in Cycling
Then there are a bunch of products for cycling which are sold to newcomers to the hobby which simply don’t work. This is very unfortunate.
There was a test run on eleven different “bacteria-in-a-bottle” that showed they were a waste of money. This link reviews that test.
Note: Prime or other chemical additives during cycling are of no use. You cannot “detox” ammonia with chemicals.
Source: Aquariumscience.org – David Bogert
Bijgewerkt op 16 June 2023 door David Bogert