Since many have asked this question, and having recently cycled my tank, I've saved all the information I got about the cycling process. I've typed out a general guidline that you could follow. Please note that this is only a fishless method as I personally prefer not to put any livestock (as hardy as they might be) through the stress and damage that the cycling process can cause them.
Fishless Cycling
Firstly, since you don’t have any live rock or sand (I’m assuming that) you’ll need something to get the ammonia going in the tank. There’s 3 ways you could go about doing that:
Method 1. You could add a medium sized raw prawn/shrimp to the tank and wait for it to start rotting (probably take it 2 days or so). A little piece of friendly advice – put the prawn in a pantyhose and then stick it in the tank as once the prawn decomposes, it’ll pretty much disintegrate and create a big mess in your tank when you need to take it out. When the shrimp decomposes, it will create ammonia (NH3), which you should start seeing on your daily tests. The NH3 will eventually spike, and then decline when the NH3 eating bacteria take over. When this happens, your nitrITE (NO2) will start to rise. Similarly this will lead to a NO2 spike at first, then NO2 eating bacteria will break it down, leading up to its decline. The declining NO2 will cause a rise in the nitrATE (NO3). At this point, your NH3 and NO2 levels should both be testing out to at 0ppm. Once you see that they have checked out at 0ppm over a few days, its fairly safe to assume that your tank is cycled. A good way to test this is by using PURE ammonia to dose your tank. This is not an absolutely necessary step but you can do it just to double check. Use only pure ammonia as I have listed in Method 2. You will need to add a few drops of the NH3 so that the NH3 levels in your tank get bumped up to maybe 1ppm. Test your water in 12-24 hours and see if either any ammonia or nitrites show up. If neither show up, your tank is cycled. Once your tank cycle is complete, you will need to do a fairly large water change to bring the nitrATES down. Just a warning about using this method: the decomposing prawn may cause a pretty bad stench (it did in my case) – so make sure the room that the tank is in has plenty of open windows/air circulation.
Method 2. Instead of using the prawn to create the ammonia spike, you can simply start off with pure ammonia. A very important thing to remember here is that you have to use PURE ammonia only – one without any additives or perfumes in it. The household cleaning stuff is perfect for this use, but make absolutely sure that it does not contain any additives or perfumes before using it! It should be free of surfactants, perfumes, and colorants. Always read the ingredients on the bottle. If it doesn't list the ingredients or say Clear Ammonia (or Pure Ammonia or 100% Ammonia, or Pure Ammonium Hydroxide), then leave it on the shelf and look elsewhere. Shake the bottle if you're not sure about it because Ammonia with additives will foam, while "good" Ammonia will not. You start off by adding X drops amount of NH3 until a level of 5ppm is achieved. This X amount of drops has to be added daily until the nitrITES spike. Afterwards follow up with ½ X (from previous step) amount of NH3 drops daily until NO2 is 0ppm causing a nitrATE peak. Once again, once both NH3 and NO2 have checked out at 0ppm over several days, and your tank is cycled, do a large water change to reduce the NO3. I personally don’t like this method a whole lot since it stresses out the tank a fair bit.
Method 3. This is basically the same as method 1. Instead of using a prawn, you can simply add fish food to the tank, and let it decompose, creating the NH3. This might take a little longer, and you might be left with lots of decaying food in the tank.
Please keep in mind that using any of the above three method creates only a certain amount of bacteria colonies capable of handling a limited amount of ammonia. So, always start to stock slowly, as rushing things might cause another ammonia spike, which is not good for the livestock you’ll have in the tank.
Let me know if you have any more questions. Also, do read the "sticky" that Max has put up regardin the SW cycle in this forum.
Regards,
Yash
