once your tank has cycled you shouldn't have to go through it again unless you move your tank or add too many fish all at once or clean the filter or do a very large water change (basically anything that could wipe out your bacteria colony could cause the tank to go through a new cycle). you can't just let your tank sit empty and not do anything to it and it will cycle. you have to add some kind of ammonia source, preferably just bottled ammonia from the store. it helps out a lot if you also add a bacteria source like live plants or some object out of an already running tank 9like some gravel or a filter or even just some water). then you have to get out your test kits and monitor the cycle and stuff.... there is a sticky and some other threads and a lot of information on the internet that will tell you in detail how to do this, just type "fishless cycle" into your search engine. alternately you could just add 1 or 2 small hardy fish and then when your test kit says the cycle is done you can gradually add more fish, but doing it this way is more expensive because you have to buy fish instead of just a 99c bottle of ammonia, and the fish might die during the cycle and even if they don't die it hurts them. anyways just do more research, there are a lot of detailed instructions out there of how to cycle.
cycling refers to the nitrogen cycle: fish produce ammonia in their wastes, and bacteria help break down the nitrogenous compounds, and lower the toxicity of the nitrogen compounds in your tank.
ammonia (fish waste broken down by bacteria)
|
V
Nitrates<----------------------- Nitrites
(removed by water changes) (broken down by other bacteria)
these bacteria are everywhere in nature, but not at quantities significant enough to handle a tank of fish waste. we put ammonia in the tank to feed the nitrifying bacteria, so they can grow and multiply.
once the bacteria are able to break down the fishes' waste efficiently enough to support a healthy tank, the tank is "cycled."
So yes, once a tank is cycled for a certain bioload, it should not have to be done again. Large water changes will not kill off the nitrification bacteria, so long as the replacement water has the chlorine/chloramine neutralized. Filter clening will not either if it done properly - if you throw all you media away and replace it with new, you may have a problem, but routine filter cleaning is a requirement, just as are water changes. Nor should moving a tank injure the cycle - I've move two tanks in the last three weeks, and will do a couple more in the next week or so - I had no problems, and expect none from the rest of the moves.
Meds and too many wrong additives are the things most likely to mess up your bacteria once they are established.
