Methods for Cycling Your New Aquarium
There are 4 basic ways to cycle your Aquarium. They are: With fish, without fish using fish food, without fish using PURE ammonia and without fish using raw prawns. For years, cycling has been done with fish. They are basically a sacrifice to your tank so that you can put the fish you actually want into it when the cycle is finished. Many have been moving to the fishless cycle and that is the one I will explain ion the most detail. I will touch on the fish cycle just in case someone still decides to use it.
First off, let me explain the cycle in lemans terms, the only way I understand it. When you start an Aquarium, you are starting with clean water, a clean tank and most of time everything is new. The newness of aquariums and their equipment is what makes it necessary to cycle your tank. When you add fish, fish food, ammonia or a prawn you are starting the first step of biological decomposition. This step feeds the bacteria that eats ammonia and turns it into nitrites. It can take 3-4 weeks for the ammonia eating bacteria to get established and consume all the ammonia that is produced or added to the tank daily. Testing for ammonia is a crucial step to be able to track the progress of the cycle.
The next bacteria to become established are nitrite eating bacteria. As the ammonia is turned into nitrites, the nitrite bacteria changes the nitrites into nitrates. It can take up to another 3-4 weeks for the nitrite eating bacteria to colonize large enough to process all the nitrites and turn them into nitrates. Again testing your tanks and tracking your levels is the only way to tell if you have enough bacteria to consider your tank cycled. The Nitrite cycle can take a little longer to get started and to finish.
Nitrates are removed by doing water changes. Some say not to do any water changes while you are cycling others say that you need to. There is a need to do a water change before adding fish to remove the nitrates. Some say water changes are not "needed" and may interrupt the cycle by lowering the levels ammonia and nitrites unless levels become overly high. Others say that water changes will not hurt and that as long as you keep adding the ammonia then the cycle will continue without a problem. So if you have .5ppm or 5ppm, the bacteria still grows at the same rate. Also, excessively high nitrates could affect the cycle time. So water changes may actually help with the cycle especially the nitrite part of it.
Now your tank is finally cycled when both your ammonia and nitrite levels read zero (0). When dosing ammonia, the ammonia reading needs to drop to zero in less than 24 hours. Nitrite values should always read 0 but a slight reading may be seen within a couple hours of dosing ammonia. As long as the levels are zero when the ammonia drops to zero the tank is cycled. As for the prawn method, once the ammonia and nitrite readings are zero and stay there for 3 days then the tank is cycled. Do a partial water change, 50% is recommended to lower nitrate levels and then test for nitrates. Your nitrate levels should be below 20ppm. If they are not then you need to do another partial water change to get them there. Remember to keep the prawn in the tank until you have your nitrates down where they need to be otherwise your cycle can be interrupted and may start a mini cycle when you add fish.
As for the number of fish you can add, this is highly debated by those that do fishless cycles. You should not stock a tank to its carrying capacity right after you complete a fishless cycle. If you are adding small fish, then half capacity should be easily supported by the bacteria in your tank. If you are adding one or two large fish, make sure that you check ammonia, nitrite and nitrate levels to insure that the bacteria are keeping up. As long as the tank is supporting the fish you put in then it should be ok to add a couple small fish every 2 weeks until you reach your tanks capacity.
When adding a prawn 1 medium sized prawn is enough for any tank up to 30 gallons. 2 shrimp for up to 60 gallon and so on. Basically for every 30 gallons you add 1 medium size prawn. They need to be completely raw, frozen is ok, but not cooked or seasoned. Also, placing the shrimp in a fine mesh filter bag can help in removing when the cycle is complete without making a big mess where you may need to do a good gravel vac to clean up the mess.
When adding ammonia you start with 3-5 drops per 10 gallon of water. Levels of ammonia around 3-5ppm is needed to establish a large enough bacteria colony to support the initial biological load. Make sure to use PURE ammonia not ones with perfumes or used as household cleaners unless it has nothing else added to it. If you are wanting to start with more fish than half a tanks capacity then you can up the dosing of the ammonia once the levels drop to 0 after 24 hours. An additional 1-2 drops per 10 gallons of water will raise your ammonia again and you will have to wait until it reaches zero again in less than 24 hours and your nitrites reach zero in the same amount of time. This COULD make it safe to add a full tank of fish but again, make sure to test your ammonia and nitrites to insure that the tank can handle the fish you put I there.
As for fish food, this is hit and miss and not the best way to do it but it works. Add about 1/16 tsp of food daily and test for ammonia, nitrites and nitrates to follow the cycle. A very small number of fish should be added when using the food method to insure that the bacteria can handle the fish and their waste.
As for cycling with fish, many fish can be used but the common choices are swordtails, platys, neon tetras and snails. Goldfish could be used but should be removed before adding your fish choice to the tank. Zebra Danios are probably the hardiest fish, and work well for cycling. Just please make sure to keep up the water changes to try and give the fish the best environment you can if you use fish to cycle.
Some very important things to remember: The tank needs to have a good amount of air going into it in order for the bacteria to thrive. Without added air, the cycle can take 3-6 months longer. Never use any type of chemical or media that is used to remove ammonia from the tank. Instead do partial water changes to control the levels if they are higher than expected. Ammonia higher than 7ppm is really the only time to worry about a partial water change in a fishless cycle. Ammonia above 0.5ppm, nitrites above 1ppm (also .5ppm) and/or nitrates above 15ppm is reason to do a 50% water change in a fish cycle. Your biological filter media should never be washed in chlorinated water. Some filters have separate biological media; some don't so refer to the package when rinsing your filter media.
One way to expedite your cycle is to put some substrate, ornaments, filter media, filters or anything in your tank that has been in a tank that has been cycled already. This is called seeding and populates much more bacteria initially and will help to shorten your cycle time, sometimes to as short as 2 weeks (and possibly even shorter). A sponge filter run in an established tank can be removed and run in the new tank along with all of the filters that you will be using in order to seed the tank. It may also help to squeeze the filter in the new tank to distribute some of the bacteria to different location in the new tank and for it to get into your filter media.
Whatever you decide to do, remember to be patient and have a good liquid regent test kit on hand to keep track of the ammonia, nitrites and nitrates. These are the main killers in a new and even established tank. A word of warning to those that decide to use the prawn cycling method! The smell is not the best smell around. If in an enclosed space it could get pretty nasty if the water takes a while to start cycling and the ammonia builds up a lot. There is also a smell associated with ammmonia dosing and if it gets too high could cause quite the odor itself. Take care to try and vent the tank if the odor because annoying or too strong or try some active carbon in the filter to remove some of the prawns smell.