Aquarium cycling is the most important part of setting up your freshwater aquarium. You must keep in mind that it takes patience. The entire process takes as long as 6-8 weeks. Don’t worry. We’ll get some fish in there before that. I know you will be eager to fill your tank full of fish. It’s only natural. You just set up you new shiny fish tank and you want to see some fish! What you might not realize is that adding the wrong fish, too fast is just a recipe for disaster. You’ll quickly have a tank full of floating fish. This can be costly, frustrating, but most importantly very cruel to your fish. Aquarium cycling is really a very simple process if you keep in mind what I said before, patience.
There Is a Right and Wrong Way to Cycle Your Tank
Please resist the urge to cycle your tank using fish on the first day. There are some sources out there that suggest this cruel method. Even if hardy fish are chosen, introducing them this early in a new tank is VERY stressful on them. The fish tank cycling method that I’ll describe is preferred by most aquarium hobbyist. For your reading pleasure, I’ll do my best to save as much chemistry as I can for another article. Alright, here we go. We’re going to demystify this whole scary aquarium cycling thing. Get your water chemistry test kits in hand.
Stage 1 - Grow Those Bacteria!
To kick off the bacteria maturation process, you’ll want to add an aquarium cycle starter like Bio-Spira, Stability, or Septo-Bac to your tank after you add your first round of water. The point of this step is purely to grow bacteria. Bacteria is necessary to change the ammonia produced from fish waste into nitrite, and finally into nitrate. This fancy process is called bio-filtration. Ammonia and nitrites can both be very harmful to your fish. Nitrates can be harmful at very high levels but are comparatively harmless. Ok, that’s it for the hard chemistry, sorry. You will want to let your bacteria mature and hold off adding fish for the first 2 weeks.
Stage 2 - Keep Those Ammonia and Nitrite Levels in Check.
Finally, it’s time to add your first fish! Yippee. In step one you have established the bacteria that is necessary to process low amounts of ammonia. However, there won’t be enough to process high levels which is why it is best to start with only one fish. You will want to choose a hardy fish as your first fish. A Zebra Danio or a Black Widow Tetra are suggested hardy first cycling fish. You should allow at least one to two more weeks to monitor your water chemistry before adding another fish. During this stage you’ll want to monitor the ammonia and nitrite levels to make sure they do not spike to harmful levels. If your levels reach the harmful range you will want to do 25%-50% water changes as necessary to keep these levels in check. I suggested doing these changes at least once a week. You’ll want to remember that water changes are the best way to fix high ammonia, nitrite, or nitrate levels.
Stage 3 - Don’t Forget About That Nitrate.
By this time your ammonia and nitrite levels should have reached minimal levels. This usually occurs about two weeks after adding your first fish, making it approximately four weeks into the cycle. Once your ammonia and nitrite levels are low you are ready to add a couple more hardy fish. Your bacteria should be healthy enough to start controlling your ammonia and nitrate levels at this point. Because of this, you can even add a couple hardy fish each week for this four week stage. With the introduction of this number of fish, you will now start to see your nitrate level quickly rise. Again you will want to do water changes of around 25% every week for another four weeks. This time the changes are to control the nitrate level. Don’t forget nitrate is virtually harmless compared to ammonia and nitrite. The biggest problem with a high nitrate level is that it can cause unwanted algae growth. Alright, you did it!! This completes the full cycle of around eight weeks. That wasn’t too tough. You have now established a good bio-filter and can start adding more sensitive fish to your fish tank.
Don’t Forget to Balance out Your Water Temperature and pH
When you bring your fish home you should always first float the bag your tank water to balance the water temperatures between the bag and tank water. This usually takes 15-20 min and is best determined by touch testing the two waters. After five or ten minutes you will want to add some of the tank water to the bag to acclimate your fish to the pH level of your tank.
42 responses so far ↓
1 Fish Lover // Oct 28, 2007 at 3:58 am
Good article!
If only people who want to have their first aquarium would read this! Just this week I witnessed a guy in a pet shop selling a little bowl with plastic plants and two goldfish, to a lady with a child. He also sold them an internal filter, because the lady insisted to “do things right”. So long as the staff at the pet shop will tell people not to worry, they can get all at once, those people will not take you seriously and many fish will be killed and many children dissapointed.
2 Eric // Oct 28, 2007 at 9:59 pm
Hey Fish Lover,
Thanks a lot! The example you gave happens way too often. Many of the retail employees are giving out all sorts of crazy advice, and they are trusted as the experts by unsuspecting buyers. I’ve noticed this in just about every big box pet retailer and even many of the smaller shops. It pays to do a little research before getting started. It’s unfortunate that many people only start looking around after they have had that poor experience. Thanks again!
3 Regina Perrier // Nov 24, 2007 at 11:59 pm
Thanks for the easy to understand directions for cycling a new tank. I’ve never had anyone explain the inportance of cycling and my fish paid the price. Wish I had this knowledge in the past!
4 Eric // Nov 26, 2007 at 9:38 pm
Hi Regina, Glad you enjoyed!
5 adge // Dec 9, 2007 at 7:31 am
can you have to much filteration in your tank
6 Eric // Dec 11, 2007 at 6:55 am
Adge, No you can’t really over filter your water. The problem you might run into is that too big a filter will create too much current in your water. It could have your plants and fish getting pushed around.
7 adge // Dec 19, 2007 at 10:52 am
eric thanks for your info appreciated
8 adge // Dec 19, 2007 at 10:56 am
please can any one tell me . The way to tell the mail dwarf gouramy from the female thank you
9 James R // Dec 19, 2007 at 7:22 pm
Our water table has recentally been introduced to chloromines. I useto completly clean my tank emptied including cleaning gravel. I added the new Cloromines a 1/4 full to be carefull with bought what was suposed to remove Ive tried several and no luck they all die I had a tank of reproducing ciclids for ten years HELP anyone
10 Manny // Jan 27, 2008 at 7:03 pm
I wish I would have read this sooner also. It’s quite disturbing to watch these little guys die. I still get mixed advice from the petshop and look to these web sites to do my own research. I was still told by the petshop that I could add fish after 1 week. I am starting a new cycling process after a bad experience with gold fish. This time I want to add tropical fish to the tank but many are schooling fish. What one fish can I add that would help the cycling process in a 20 gallon tank?
11 Eric // Jan 28, 2008 at 10:46 pm
Hi There Manny,
Don’t worry about the schooling nature in the beginning. You can start with one and then add more of the same over the next couple of weeks. The trouble you get into without keeping some fish in schools is the way they get along with tank mates. Alone, it’s not that big a deal for a short time. Zebra Danio’s are very hardy fish and are very commonly used as starter fish. You’ll still want to leave it set up for a couple of weeks total before adding the first one.
12 Manny // Jan 29, 2008 at 2:04 am
Hi Eric, thanks so much for the great advice! some petshops don’t allow you to buy less than 3 fish when they are schooling fish. Any particular pet shop that you can think of that doesn’t do this? Is it ok to add 3 Zebra Danios after the second week of cycling?
13 Eric // Jan 29, 2008 at 9:31 pm
Hey Manny, Most locals should suggest 3+ but still sell them as singles. Petsmart should sell you one if you are near one. Zebras should only be a buck or so. A 20 gallon tank should be able to handle 3 after the first two cycling weeks. Zebras are small fish, but you can even pick out the smallest ones. It isn’t the number as much as the mass of the fish and the waste they produce.
14 Manny // Jan 31, 2008 at 8:27 am
Thanks again. One more question. After a month and the addition of 3 or more Danios what would you recommend, max for a 20 gallon tank if I stick to smaller fish? I would like to add a bottom fish a month after I put the Danios in. Would that be too much for a 20 gallon? I know it’s a matter of waste but it almost seems like the question is more about how much maintenance on is willing to do and how often.
15 Eric // Feb 2, 2008 at 10:30 am
You’re welcome Manny. I don’t know if you saw this post, but it’s probably worth a quick read.
http://www.fishtanktutor.com/how-many-fish-beware-of-the-rule
You hit it on the head with the waste/maintenance comment. The only other thing to consider is whether or not the tank is too crowded. I would suggest no more than 10 small (2″ or so) fish in a 20 gallon.
16 Lynda // Feb 12, 2008 at 10:39 pm
Hi there,
I currently have two black tetras in a 5 gallon tank. I notice that they do not like light at all and will hide and change color when it is left on, even for just a few minutes. I have two live plants in my tank and was wondering how I can give them some light without irritating my fish? Would a colored bulb (say blue or green) be ok for both fish and plants?
17 Eric // Feb 17, 2008 at 4:37 pm
Hey Lynda,
I don’t have much experience with different color bulbs. I would say it depends on the individual bulb. Some are designed for 50%/50% daylight and nightlight. Others are designed to put off nightlight only. My only fear is that the nightlight only versions won’t put off the full spectrum of light to give your tank what it needs.
You’ll just want to check the packaging to be certain.
18 David // Feb 22, 2008 at 4:17 pm
My friend has a aquarium but no internet, he wanted me to find out if he goes months without doing a water change and then he decided to do one and all of the waste and stuff was floating around in the water he wants to know how often he can do a water change to get it back to normal. Thanks
19 Eric // Feb 24, 2008 at 2:57 pm
Hi David,
Take a look here.
http://www.fishtanktutor.com/aquarium-water-changes-are-they-really-necessary
20 Josh // Mar 3, 2008 at 2:40 pm
Eric,
You suggest 2 weeks before adding a fish to a new aquarium. How long should you wait to add live plants to a new tank?
21 Amanda // Mar 4, 2008 at 2:08 am
Hi, Eric. Sadly, I didn’t know about the cycling process before I bought a few different kinds of gourami. After a couple weeks, the only ones who are still living are the dwarfs. I have them in a smaller tank now so I can keep it incredibly clean, but will this be enough to keep them alive until my tank has cycled? Do you have any suggestions as to what I can do to not lose my last survivors?? Thanks, and I am so thankful to have found your article…just wish I would have found it sooner!
22 Superbeanie // Mar 5, 2008 at 8:31 pm
hi, i have a 75 gal tank. i kept jack dempseys for 2 years just fine. i inherited the tank and didnt know anything. i recently got rid of the dempseys bc they wouldnt quit spawning. babies everywhere all the time. i did an 80 percent water change and changed the gravel. (the old stuff was painted and it was peeling off) i put in some natural unpainted gravel. i didnt change the filters on the spillway filter but did clean out the tubes. do i still have enough bacteria? im going to wait to get new fish (about a week). im going to get tetras and platies and some snails. will they be ok or do i have to get a bacteria jumper? my ph is 7.6 one day after water change and everything else is fine (no fish in there)
23 Eric // Mar 6, 2008 at 7:13 am
Hi Josh,
You can you can add your plants right away. They aren’t stressed by the same things that fish are.
24 Eric // Mar 6, 2008 at 7:19 am
Hello Amanda,
You hit it right on the head. The best solution is very frequent, PARTIAL, water changes. Make sure you are testing every day or two. Also, in case you don’t know, water changes should be done by syphoning the bottom of the tank to get the waste out. Only part of the water should be taken out. Check out the post below for more help on water changes.
http://www.fishtanktutor.com/aquarium-water-changes-are-they-really-necessary
25 Eric // Mar 6, 2008 at 7:26 am
Hi there Superbeanie,
I would add your new fish slowly. Start with one or two, and then work your way up over the next couple of weeks. Sounds like your good bacteria has been pretty disrupted. You probably don’t need the starter since there still should be some, but it couldn’t hurt.
Your tank won’t register any negative readings now because there isn’t any waste yet. Once you start adding the fish back you’ll probably notice the spikes. Just keep a close eye on the readings. As you see spikes, stresses on your fish, you can do partial water changes to keep it under control.
26 Superbeanie // Mar 6, 2008 at 11:12 am
i just did a ph and it is 8.6. i put some driftwood in it. how long will it take to bring it down below 7.5?
27 Eric // Mar 10, 2008 at 7:57 pm
Superbeanie,
Using driftwood will have a lowering affect but I don’t know if it will be enough to get you there quickly. Take a look here at the article and comments. I would suggest using peat moss.
http://www.fishtanktutor.com/be-careful-adjusting-your-aquarium-ph
28 anon // Mar 17, 2008 at 10:39 am
This has really helped me learn about how to do everything for when I get a new aquarium. I was told by my dad to learn all there is to know about aquariums, filters and so on before I could get one of my own. I now know exactly what to do when I get my first aquarium.
Thanks a lot!
29 NT // Mar 18, 2008 at 12:58 pm
Hi, how do I do a fishless cycle with ammonia?I just don’t know how to start. Do I just fill the aquarium up with water, add the ammonia and then wait?How will I know when it’s cycled?I got a 400L tank.
30 Kim // Mar 19, 2008 at 11:12 pm
Hi, I am a new freshwater aquarium owner. I set up my tank 4 weeks ago. It is a tall 47 gallon tank, 20″ wide x 18″ deep x 27 1/2 ” tall. I have a double wheel Bio filter and a bubbler. My amonia levels are still too high to add fish (ho hum). Reading 2.0 on my kit card. I do have a blue crayfish in the tank for about 3 weeks now and she is doing just fine. Any thoughts on getting the amonia level down? Is the tall tank an issue preventing appropriate cycling? Maybe the top (location) filter cannot circulate the tall tank? Advice????? Want want fish fish!
31 Kim // Mar 19, 2008 at 11:19 pm
PS I did add a bottle of Stress Zyme to the tank per instructions and did a 20% water change so far. I have been told not to do any more water changes until it cycles.
32 Eric // Mar 20, 2008 at 8:23 pm
Hi NT,
Take a look here.
http://www.fishtanktutor.com/aquarium-cycling-without-killing-your-fish
Basically you use bacteria starter and introduce your fish very slowly, 1-2 a week or so.
33 Eric // Mar 20, 2008 at 8:28 pm
Hello Kim,
I’m not sure why your ammonia level is high without any fish. The fish waste is what really drives those levels. I wouldn’t think one crawfish would put off enough waste to raise it much. My suggestion is bacteria starter. That will help you start building the good bacteria. This good bacteria is what you need to naturally work on your ammonia.
34 Manny // Mar 31, 2008 at 7:31 pm
Hi Eric, I am reporting back saying that it seems this time around I have succesfuly set up the tank. I am up to 7 Tetras. I didn’t go with the Danios. I did have one question about some of the happenings in the tank. All the chemistry in the tank seems to be great. However, I get a lot of unsightly bacteria on the glass, plants and other decorations. The first time around I brushed them off with a little brush and then did my gravel cleaning. After a week they are back and more prominent on the glass. Any suggestions? I used Cycle when I first put the water in.
35 Eric // Apr 5, 2008 at 9:34 am
Great to hear Manny!
The algae on the glass is no big deal. It’s common for a newly set up tank. I know it’s sort of a pain, but it will slow down with a little time after your tank completely stabilizes. Just scrape or brush it off until then.
36 Kathie Kennedy // Apr 14, 2008 at 2:37 pm
Hi Eric,
Thanks for telling me about this but I have a big problem My fish are in the 10 gal tank now and the tank is where I have to put the 20gal and in order to move them I have to empty them. Can you tell me how to safely move my fish? I am putting my phone number here. 954-742-3538
If you can please call me, collect will be fine.
Thank you
37 Eric // Apr 16, 2008 at 9:32 pm
Hi Kathie. Just remove most of the water. Leave just enough for your fish to swim. Move the tanks. Then fill them back up.
38 wayne // Apr 18, 2008 at 9:55 am
hi i have recently decided to upgrade from my 9 gallon tank to a 45 gallon tank would the water, substrate and filter media from the 9 gallon tank be enough to kickstart my new setup so that i could transfer my fish straight away? thanks wayne
39 Becky // Apr 20, 2008 at 5:39 pm
About a week and a half ago, I decided I wanted a couple goldfish. So I went to the pet store, talked to one of the workers. She told me that the two goldfish I wanted would be fine in a 10 gallon aquarium, but said I should have it set up for 24 hours before putting fish in. So I got a 10 gallon kit, went home, followed the instructions, and had it all set up and running for 24 hours before I went back to the store for the two goldfish I wanted, brought them home, and put them in the tank.
I did a 25% water change on friday, and since then, the water’s been getting cloudy - which is why I started poking around online. So now I realize that I did everything the wrong way, but is there anything can I do now to help the situation, or do I just have to keep my fingers crossed that they’ll survive the cycling?
40 Eric // Apr 20, 2008 at 9:48 pm
Hi Wayne,
It certainly would. It’s not the amount of water that matters. It’s the amount of waste from your fish and plants. You might just add new fish slowly as your new tank catches up. It really shouldn’t take long though.
41 Eric // Apr 23, 2008 at 9:28 pm
Becky,
The key is a close eye on things at this point. You’ll need some test strips. Test daily keeping a close eye on ammonia and nitrates. If they are anywhere near the stress level shown in your kit, do a large (30-50%) water change until you see only slight readings. After a couple of weeks depending on the size of your fish, you’ll notice that the levels will start to take care of themselves.
42 wayne // Apr 25, 2008 at 7:41 am
thanks eric i added substrate, water and filter media from my old tank its been in there for about a week now ammonia levels are showing o-o.6
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