Before we can have a discussion of fishless cycle, we need to make sure everyone understands what we mean by the term "cycle." The Nitrogen Cycle is the most important thing we need to understand as fishkeepers. It's chemically a very complicated process, but here's the Cliff's Notes version. Fish produce ammonia (urine), the problem is that ammonia is very toxic. Now, in nature, the currents in the water just carry the waste away until it's processed. In the home aquarium unfortunatly, we don't have that luxury, what we do have however, is millions of little allies. Those allies are in the form of bacteria, probably of the genus Nitrosomonas, these bacteria take the bad ammonia and convert it to nitrite. Great huh? Not really. Nitrite is just as, if not more toxic than, ammonia, so the process repeats itself, just with a new set of bacteria, probably from the genus Nitrobacter, and the end product is nitrate which is far less toxic. That isn't the end though, we still need to get rid of that nitrate because it's still toxic, just not as bad as the others. The only effective way to get rid of nitrate is frequent partial water changes, so don't neglet your tank maintenance! For a bit more in depth discussion of the Nitrogen cycle, check out this link.
Now, what do we mean by "cycling" a tank? Cycling a tank is simply building up colonies of bacteris that are large enough to handle all the ammonia your fish produce. Now, the nitrifying bacteria are all around us, in the air we breath and the water we drink, all we need to add is a food source (ammonia) to get them to multiply in our filter. There are two ways of going about this. The first is the "traditional" method of putting a few hardy fish in the tank and hoping they survive the stress of the cycle. The second method, the point of this writing, avoids the stress on the fish by artificially adding ammonia.
How do I fishless cycle?
As I mentioned above, to cycle a tank you need to add ammonia. If you do choose to reduce the stress on your fish, and fishless cycle, the first thing you need is a source of ammonia. This one's pretty easy, just run down to your local grocery store and pick up some clear ammonia. Make sure it's clear ammonia with no perfumes, surfactants, or other additives; the label should say something like "clear" or "pure" ammonia.
Now that you have your ammonia, the fun begins. Add ammonia until your test kit reads 5ppm (you do have test kits right?). Since different brands off ammonia have different concentrations, there is no formula for "x amount of ammonia per gallon," you just need to keep testing. Once you've added you ammonia, test daily and try to keep the level above 5ppm. The exact amount isn't really important, just make sure the bacteria have a constant supply of food.
Every few days, test for nitrites. After a few days (or maybe a few weeks) you should see your nitrite level slowly rise, peak and then start to drop off. As the nitrite is dropping, you should start seeing nitrates. Once your nitrite registers "0" your tank is cycled!
Ways to speed up the cycle.
There are a couple of ways to speed up the cycle. The first is simply to raise the temperature of the tank. Chemical reactions are accelerated at higher temperatures, which causes the bacteria to divide faster. Be careful not to raise it too much however, over a certain point, bacterial growth is impeded. I've found the mid- to high-eighties work well. Obviously this won't work in a tank that is already stocked, you don't want to end up with cooked fish!
The second way to accelerate your cycle is to add "seed" bacteria to your tank. The more bacteria you have, the faster they'll be able to multiply. There are a few ways to add bacteria, the easiest (and cheapest) way is to take some gravel or filter media from an established disease-free tank and add it to your own. It's also possible to go down to your LFS and buy some sort of bacteria-in-a-bottle additive (Cycle, Stress-Zyme, etc.). It is the opinion of this author however, that these products are designed to do nothing more than part you from your money.
Why Fishless Cycle?
Perhaps the most common question asked of me when it comes to fishless cycle is, "Why bother? Why should I bother with all those test kits and adding ammonia and all that other stuff, when I can just throw in a few hardy fish and let nature take its course?" Well, as impolite as it may be, I always answer this question with a question. What is a "hardy" fish? Certainly, it's not a fish that's immune to ammonia posioning. All fish are hurt by ammonia, it's just that "hardy" fish are more likely to survive. As fishkeepers however, our goal shouldn't be that our fish merely survive the stress, our wish should be that our fish thrive . It's our duty to provide the best environment possible for the creatures under our care. Posioning our fish with toxic chemicals such as ammonia and nitrite is not the best possible environment; especially when it could be avoided through a process as simple as fishless cycle.
Thank you for taking the time to read my rant. If you have any questions, feel free to e-mail me , or better yet, post on the message board.
By Josh Wright