I saw this discussion being skirted in another thread, and i've honestly been confused before by all the different types of cycling that are touted and denigrated by different folks.
I'm gonna try to aggregate as much info about cycling into one thread (and keep the highlights in this post) so that other people have a good jumping off point in the future.
What is cycling?
Cycling is the process of taking a new tank, and building up bacterial colonies that neutralize toxins in the water.
Toxins? But i only put water into my tank!
All animals (land, sea, and air alike) take in nutrients, and expel the substances that they either don't need, or that have become toxic through the digestive processes. The primary toxin that concerns aquarists is ammonia.
Can't i just let my tank sit for a little while to build up these colonies?
While certain bacteria may grow if you just let your tank sit, these bacteria aren't the beneficial toxin reducing bacteria. The bacteria need food, and the food is ammonia. Therefore, you need a source of ammonia.
Ammonia, Nitrate, Nitrite... what does that mean?
Ammonia is the fish waste that is released into the water. This ammonia is transformed by a certain type of bacteria into nitrites (with an 'i'). While these nitrites are less toxic, they are still a toxic substance to the fish. A second stage of bacteria then consume that nitrite and turn it into nitrate (with an 'a'). This nitrate is much less toxic than ammonia or nitrite, so it is preferred that the ammonia is converted to nitrate eventually.
If Nitrate is good, why do we test for it and try to keep it low?
Nitrate is still toxic in large enough doses, similar to carbon monoxide poisoning for humans. Therefore, keeping track of nitrates balances between the health of the fish and giving plants some of the nutrients to help them grow well.
Types of cycling:
Fish (Old School) Cycling:
This involves a fairly simple process of sticking fish into a new tank in order to build up the ammonia and thus start the growth of the bacterial colony.
-It's really simple. 1) Fill tank 2) Add fish 3) Change water regularly
-You don't have a tank sitting around empty for 2 months
-There is a constant source of ammonia
-Water changes are imperative, or you'll kill your fish
-It's morally questionable. You're exposing some fish to increased levels of toxins for a prolonged amount of time.
-Many fish are too fragile to be used for cycling. There's no way you could keep the ammonia balanced in such a way to keep the fish alive and cycle the tank at the same time.
Bio-aided Fish Cycling:
This involves adding a starter colony of bacteria to the tank while cycling as above in the fish cycling
method. This can be added using a bio-active solution that you can buy at your LFS (see Cycle
). You could also add a filter medium from a cycled tank by pulling a sponge or filter floss and putting it in the new tank.
-It's faster than not having a bio aid in the system
-It puts less stress on the fish, as there is a good base colony of bacteria present
-It still puts stress on the fish, even though it is less stress than an aid-less cycle
-You either have to buy the solution (which can be expensive) or have access to a cycled tank in order to use this method
This method replaces the fish with a different ammonia source. You could use anything from liquid ammonia to fish food to frozen shrimp. Anything that creates or actually is ammonia. This method requires a little more advanced monitoring of the water parameters so that you don't undo the work you've done.
-You're not stressing your fish
-You are actively working on your tank even before it's ready for fish
-You have a very good idea of exactly where your tank is in its cycle
-You're adding the ammonia, so you have to be very diligent
-This is a relatively intensive process, having to add ammonia daily and take test measurements daily at the least
Bio-aided Fishless Cycling:
Just like the bio-aided fish cycling
, this acts to speed up the process by introducing a mature bacterial colony into the picture.
-Faster than regular fishless cycling
-You are still actively working on your tank
-You are still aware of where the tank is in its cycle
-It is still a relatively intensive process, but it lasts less time than the regular fishless cycle
-You still have to be diligent. If you forget too much, your bacterial colony will start to die.
This is somewhat a compromise between fish and fishless cycling. This method works off the fact that the toxins in play in cycling are absorbed by plants. Therefore, if you pack a ton of plants into a tank, they'll absorb any toxins that aren't consumed by the bacteria, alleviating the issues with stressing fish out.
-The fish aren't stressed out by increased ammonia and nitrite levels
-You get to add fish and plants almost immediately
-You don't have to add your own ammonia, but you can if you want
-You can't pack tons of fish into the tank. Plants aren't magic, they can only absorb so much of the toxins before they can do no more
-Certain styles are incompatible with this method (iwagumi for one). You need a certain level of plant mass or it is just a fish cycle
-This cycle is relatively slow, since the plants absorb much of the toxins
Alright, so i've selected my method, but how do i know what's going on in my tank?
The easiest way to monitor your tank is to buy a test kit. There are two types of kits you can get, test strips (dipping paper into the water and looking at the color), and liquid (measuring out some water, adding some reactive chemicals, and looking at the color). Liquid is much more accurate and precise than the test strips, but neither is very accurate if the kit has expired (yes, they expire).
I bought my test kit and followed the instructions, but the numbers that i get mean absolutely nothing to me.
Yeah, yeah, maybe that's because i haven't gotten there yet! Ya think of that wiseguy?
Most of these methods advocate testing on a daily basis, and most people advocate writing down the numbers you get for your big 3 parameters: Ammonia, Nitrites, Nitrates. If you were to test your water before adding any ammonia source, you should get 0ppm for all three. Once you start your method, you'll see the two stages of the cycle at work.
Your awkward pauses at every new point are getting annoying! Explain what happens next!
What you're going to see at the start of the first stage of the cycle is a heavy spike in ammonia. Your ammonia levels will be high, and your nitrite and nitrate levels will be around 0ppm. This is because there aren't enough bacteria to eat that ammonia, so it just sits in the water, ominously. As the first stage progresses, the ammonia eating bacteria begin to colonize your tank, and you'll see a change. Now, the ammonia levels will start to come back down to lower levels and the nitrites will start to spike. You know that your first stage of cycling is over when your ammonia levels are unreadable and your nitrite levels are high.
Alright, so stage one is ammonia to nitrite. What's stage two?
Stage two comes shortly thereafter. It involves the waste from the ammonia bacteria (nitrite) being eaten by nitrite eating bacteria. These nitrite eating bacteria will make nitrates. The beginning of the second stage begins at the end of the first stage. Ammonia will be unreadable, nitrites will be relatively high, and nitrates will be relatively low. As stage two progresses, these nitrite eating bacteria start to colonize, and you will see yet another change in your readings. Ammonia will stay unreadable, but your nitrite levels will begin to drop and your nitrate levels will begin to rise.
My nitrite levels are dropping. I'm done, right?
NO! You're very close, but you're not there yet. Once your ammonia and nitrite levels are undetectable for a couple days, you can be assured that your cycle is finished.
Anything else you wanna tell me?
Not particularly... I'll let the actual smart people on the board take over from here. Oh, oh... I've got a good one. This material is only the best of my knowledge, so don't take it for scripture. I may have missed something, or i could be just plain wrong.