You may think fish keeping is about fish, but actually it's about bacteria.

"New Tank Syndrome"

For a lot of people, their fish keeping experience starts like this:

They buy a tank, a stand, a filter, a hood, lights, selection of plants, rocks, diver with genuine bubbles... They add water (which they have carefully dechlorinated and got up to temperature). And then they make their first (and biggest) mistake: they buy some fish. This might be a week later, but apart from checking the tank isn't leaking and all the gizmos are working, leaving the tank to stand for a week doesn't accomplish much.

The problem is ammonia: Fish pee ammonia. Not only that, but their poop also breaks down to ammonia. So before long, your new fish are swimming about in a toxic pool of ammonia.

Tragically, ammonia is deadly poisonous to fish. It inhibits their breathing, rather as carbon monoxide does in humans, and they slowly start to suffocate. Don't believe anyone who says there's a "safe" level of ammonia for fish - I'm sure there's a safe level of carbon monoxide, but I'm not going to rent a house that has it!

Beneficial Bacteria

This is where your bacteria come in: fortunately, certain types of bacteria can break down ammonia into a less toxic substance called nitrite (that's with an 'i' - note the spelling, it's important) aka NO2-. After a few days, this "ammonia-eating" bacteria start to grow in your tank, particularly your filter and gravel, and drop your ammonia levels to zero. Phew!

But your fish aren't home and dry: nitrite is less toxic than ammonia, but is still toxic and can still kill fish. Thankfully, another sort of bacteria starts to grow in your filter and gravel (albeit a little more slowly than the "ammonia eating" bacteria). This beneficial bacteria breaks down nitrite (NO2-) and turns it into nitrate (NO3+) - note the 'a'. Nitrate is only harmful in quite high levels, which can be controlled by regular partial water changes, and is useful to aquatic plants as a fertiliser.

This process is called the Nitrogen Cycle, and in fish-keepers jargon, a tank where the bacteria are happily munching on ammonia and nitrite is said to be "cycled". In summary:

Fish waste --> ammonia --> nitrite --> nitrate, which plants use to grow.

The beneficial bacteria are what make your tank safe for fish. Although present in the water, they are largely found in the gravel or sand in the bottom of your tank and in the filter. As well as ammonia, they require a good source of oxygenated water to grow.

How to "Cycle" Your New Tank

Traditionally, the way of getting around this problem of establishing the beneficial bacteria is to put just a couple of really tough fish in your new tank and wait 8 weeks before adding a few more fish.

Unfortunately, even if the fish survive (which is a pretty big "if" ) they have to endure weeks and weeks of first ammonia poisoning and then nitrite poisoning. They may survive, but they may never enjoy good health or live as long as they should and I personally feel it's a welfare issue.

But there is a better way: Fishless Cycling. If you follow this link, and another you can read up on the technique.

The advantage to Fishless Cycling is that it effectively grows your bacteria before any fish are damaged. By the time your ammonia and nitrite readings are zero you'll have plenty of beneficial bacteria to break down the waste from as many fish as you want in your tank and can fit.

Can a Cycled Tank Un-Cycle Again?

Even in an established tank you can get ammonia or nitrite "spikes", usually because something has killed off your beneficial bacteria. This could be for several reasons:

1. You forgot to dechlorinate your water when you did a water change. Chlorine kills bacteria!

2. You over-cleaned your tank, particularly the filter media and gravel, particularly is you didn't dechlorinate your water and particularly if the gravel or filter were out of the water a long time.

3. Some filter companies recommend you change the filter media every month (Well they would say that, wouldn't they??? ). Not only is this an expensive waste of time quite often (filter sponges usually just need a rinse in some old tank water), you could be removing the beneficial bacteria. If you want to replace a filter insert, leave the sponge or floss in the tank for a week or so beforehand.

4. A power-outtage stopped your filter or pump from working for a couple of hours (bacteria need oxygenated water to survive).

5. You over-loaded the bacteria in your tank's ability to break down the fish waste, for instance by suddenly over-stocking your tank, particularly with messy fish.

6. A tub of food has fallen into the tank and gone bad, thus overloading the beneficial bacteria's ability to cope.

How to Save the Day (and the Fish) with an Un-Cycled Tank

OK, so you didn't do Fishless Cycling or you did scrub out your matured tank and now your fish are dying and nothing's breaking down that ammonia and nitrite. What do you do now?

Here's what I do to give my fish the best chance:
1. Immediately do a 10-15% water change with dechlorinated water and continue to do this at least once daily until your tank is cycling (i.e. ammonia and nitrite are at zero).

2. Test the water daily for ammonia and nitrite until the values are holding at zero for several days running. If levels are high, do an immediate, extra water change.

3. If at all possible, get some matured filter media and/or gravel from a matured tank and put it in your tank, suspended in an old stocking. This will hopefully impregnate your new tank with the beneficial bacteria. One lady successfully used floss from a relative's fish pond to colonise her new tank! (you have to be careful that what you use is clean and free from pathogens, of course).

4. Keep good aeration in the tank both to help the fish a little and to oxygenate those beneficial bacteria.

5. Avoid using medications, if at all possible, as many medications kill off beneficial bacteria. Your fish may well get ick, fungus or other infections due to the stress of the ammonia and nitrite but the priority is to get that water quality as good as possible.

6. If you have delicate fish in the tank, such as plecos, corys or other bottom dwellers, tetras, pencilfish etc. try to re-home them temporarily, such as asking the Local Fish Shop to look after them until your tank is cycled (after all, chances are that they got you in this mess in the first place).

7. Live plants can directly use ammonia, so if you can, put some cheap aquatic plants in the tank, such as elodea or giant vallis.

8. Don't feed your fish at all if your ammonia readings are high, and only feed bare minimum rations every other day, until the tank cycles. This will cut down on the ammonia the fish produce. Since fish are cold blooded creatures and don't need the calories of a mammal they can go several days without food anyway, and the occasional fast is good for them. Your fish may not be very hungry anyway so do be careful not to feed more than the fish can eat and clean up uneaten food immediately, before it rots and produces even more ammonia.

9. Only clean the gravel superficially, of obvious dirt and uneaten food. You want the bacteria to colonise it and actually start to grow. Also, don't swap out your filter at this point - if it gets blocked, just clean it enough to unblock it, in used tank water.

Frequently Asked Questions on New Tanks and Cycling

Why didn't my Local Fish Shop (LFS) tell me any of this?

Good question. Probably ignorance - people are amazingly ignorant of the Nitrogen Cycle, which is shocking when you consider its importance. IMHO, more people have killed more fish due to bad advice from an LFS than anything else. Temperature and pH are most often blamed when ammonia and nitrite are by far the more significant problems. When it comes to buying fish and aquarium products: Trust No One. Double-check everything you are told and plan in advance.

The guy at the LFS sold me some "Instant Cycle" product that contains the beneficial bacteria. Do I still need to cycle my tank?

There are a variety of bacteria products on the market which claim to be able to increase the speed at which your tank cycles (note: none of them claim instant cycling, whatever LFS employees may say). Personally I can't see how they could work, since the bacteria require a source of ammonia and oxygenated water, but even if they can be held in some sort of "suspended animation", that still doesn't get around the fact that they can't instantly colonise your gravel and filter. Colonisation takes time!

The LFS sold me a product that locks away ammonia. Can I use that to save my fish?

That's a difficult one. Ammonia is deadly to fish and you want it out of your water ASAP. However, products that lock away ammonia have some major disadvantages: For a start, they mess up your water test readings so either look negative when they aren't, or look terrible when they aren't so bad. Secondly, if the beneficial bacteria still aren't established, and the ammonia from fish keeps rising, it could over-shoot the ability of the product to lock it away and you get a sudden (and deadly) ammonia spike (which of course you can't reliably test for). Thirdly, theoretically, "locked" ammonia can't be utilised by the beneficial bacteria and may possibly retard its growth.

Why did my pleco die while my gouramis and danios were fine?

There is a big difference between "alive" and "fine", but even so, the reason that your pleco died is probably because he was less able to get to the top of the tank where the oxygen levels are highest and the ammonia levels a little lower. Danios swim near the top of the water and are famous for their survival ability (I believe they used them in nuclear experiments in the 50s). Gouramis and bettas can directly breath air, through their labyrinth organ.

The LFS guys said he'd never heard of this "Fishless Cycling" nonsense and he's been in fish-keeping for 40 years. He said to cycle with danios. How come?

Fishless Cycling is a relatively new technique that has only really been talked about since the age of the Internet. It is a lot safer for fish and avoids suffering. It also prevents fish being subtley damaged in a way that may affect their health for life. However, people may be tempted to stick to what they know "works", possibly not really understanding the welfare implications, or the great advantages to cycling fishless.

I have a betta in a fish bowl. Can I cycle without a filter?

You certainly can (and should). Just follow the same procedure as for a larger tank - the bacteria should colonise your gravel. Since the bacteria really need oxygen to do well, adding an air-pump with an air-stone, or better yet, a small tank filter of some kind, will improve things even further.

But my biggest problem is that algae that's taken over my tank!

Algae in an un-cycled tank is a trivial cosmetic problem that you should worry about later. Algae doesn't kill fish - but algae can directly use ammonia, which is probably why algae-covered tanks are assumed to be unhealthy tanks.

But I tested my water when I first set my tank up and it was fine!

You won't get ammonia or nitrite unless you have fish, or an artificial source of ammonia (such as that you add during fishless cycling).

Won't carbon in my filter remove all the toxins anyway?

Carbon may temporarily remove some of the ammonia, but it won't touch nitrite and only works a few days anyway, and then everything can leach back into the tank again! There are no short cuts to growing beneficial bacteria (other than using a matured filter and gravel) to cycling your tank.

But it's so boring waiting for my tank to cycle. Can't I just add a couple of fish now?

If you are impatient just remember that it's even less fun watching fish die. So spend your time designing your "aquascape", soaking your bogwood and rocks, establishing your plants and checking that everything works fine. Also, get on the Internet and read up about the species you'd like to get, checking with your LFS's to see what they have in stock. Buying online is often cheaper and more convenient, so get to know your favourite outlets now.

Yeah, but what exactly is "Cyling a Tank"?

If you ask this question now, you'll get a custard pie in the face

RTFM!

This post has been edited by Alien Anna: Sep 4 2003, 12:58 PM

Hmmmm..... - do you feel better now anna? lol

....-you have been busy - not sure if its a rant or an artical lol

I'm totally with you you on the fishless cycling

Though I'd also stress the importance of regular testing of the water especially in the early days...

I'm sure william could be interested in using this on the site

For my new tank I filled it and left it for a week then I got fish BUT I also bought some bacterea to start the cycle, this makes it fairly safe for the fish as the cycle complete's it's self. The only trouble I had was at the very end of the cycle when the nitrites spiked to levels my chart wasnt even able to read. Also at this time I had a very pregnant female that had just gotten over a bad case of mouth fungus, so she didnt make it and she got horribly sick again from a missing scale by her cuadal fin. She didnt make it along with some small harlqiun rasboras that got constipated or wouldnt eat. I believe the fishless way of cycling may have the same effects when you add some fish to it so both ways seem to work but I learned the very hardest way not to add fish to a 24 hour old tank with no bacteria living in it! Also befor you add new fish to a tank you should do a gravel vacume and 20% water change the day befor. I would also suggest you don't add more then 3-5 fish at a time depending on their size.

Hmmmmmm
Everyone can shoot me now.

I've never cycled a tank in my life. I keep and breed blue rans, gold rams, and discus. Have never lost a fish to odd effects of ammonia, and continually set up new tanks and move occupants in the same day. Normally without acclimateing them............

The trick is understocking a tank at first and doing daily/every other day water changes. I'm sure a few of my older tanks are "cycled" but not on purpose..........as long as the water stays clean I don't think the fish care about the bacteria.

Simply put, this is called, "Cycling with Fish."

My 29 gallon tank just finished cycling in just 3 weeks. I used a Betta and 5 White Clouds. I wasn't expecting it to be so quick. I tested the water twice a week. It took a week and a half just to get an ammonia reading. A week later the ammonia was at 0 and nitrites were up. And on Sunday I got 0 ammonia, 0 nitrites, and 15ppm nitrates.

I'm looking forward to getting more fish this week. I got the White Clouds with the intention of keeping them, but it turns out I don't like them and will see if the LFS wants them. My wife and I just don't find them interesting. I want to put a few corys in and then when the tank stabilizes to that load then swap out the WCs for some rummynoses. I don't know if the tank will hold much more than 8 tetras, 4 corys, and a betta, but I'd also like to get 3 small gouramis or maybe a killifish in there.

Karl

i made a bullsup listening to the staff who knew f-all but its sort of ok now, ive had my tank for about 3 weeks and used one of the 'cycles' in 24h tablets (tetra bactezym) and added 2 albino tiger barbs and a bronze cory (yes i know the numbers are too small but the staff ... ) and experienced my spike this weekend (have a thread in the beginer section)

Hi Anna,
Thanks for the great info. I am just having a problem with the links you supplied however. I am interested in fishless cycling, is there any chance you could post a little more info on the procedure?

Thanks

Edit: Sorry I just found other topics refering to this. Ignore me and I'll just go away...

This post has been edited by scotto: Apr 5 2006, 12:49 AM

So a tank is fully cycled once the nitrite and amonia are at trace levels?

Sorry I'm a bit thick

Not really. A better definition would be that a tank has finished fishless cycling when it can convert 5ppm ammonia to nitrIte and then to more harmeless nitrAte in 24hours. At this point you change around 80 - 90% of you tank water and then fully (yes fully) stock your tank. Some people are more cautious and just add a few every week but I completely stocked from day one and have only suffered 1 loss.

ps mods this must be pinned surely. Annas post answers about 50% of posts that appear everyday in the beginners section!


This post has been edited by jonesyUK: May 14 2006, 06:19 PM

thanks for the reply

thanks for the info

high just read yur faqs on cycling a tank nak think it is exelent and realy helpfull
ive just got a few questions i wonder if you could help me with????

I have a 180l tank and have had it for 3 years now and basicly have played with fishkeaping and got very dis hartened due to my lfs giving me bad advise

they would tell me things for a sale (as I know now) i.e "this blue light makes fish look nice" wich it did but it also filled my tank with alge and "you are loosing plants because the fish are eating them that is what they do"

anyway to cut a long story short i found a new shop and the advise is exelent and they shuddered at the advise i had been given and put me strate on a lot of things but still areing on the side of caution (once bitten twice shy) ive started again with my tank

it is planted with substrate, plants CO2 and all is going well plants are growing and fish seem happy.

Ive got a water testing kit for crimbo and now test water my self. what i would like to know is what are the ideal readings for these tests for a happy aquarium and fish.

the fish i have are ;- 2 clown loaches (had from start of tank 3 year ago)
4 black widdows
4 male guppys
1 penguin
1 lemon tetra

recently bought 5 neon tetras yesterday
they all seem happy and i havent lost any since the change touch wood

the tests i have in my kit are ;- Amonia
PH
Nitrate
Nitrite
I have also been advised to remove my nitrate filter sponge from mecanical filter as the plants need the nitrate.
The filter also has a carbon sponge and some people tell me to leave it in (lfs) and others tell me to take it out/ which ot these is the best for a happy aquarium?

please help i would be greatfull of you advise

An excellent article, and well worth pinning I would say!

I am just about to upgrade from a 60 ltr Aquastart 500 to a 260 ltr (I think!) Fluval Vicenza. My question is this:

When cycling my new tank, would it be advisable to remove the sponge from my old filter and suspend it in the new tank? If so, would it be OK to replace the sponge in my old filter with a new sponge for the remainder of the time I shall be using it? I perhaps should mention that I have two filters in my old tank, one of which is three stage with carbon, sponge and bio-rings. So even if I remove the old sponge from that one and replace with new, there is still the second mature filter and also the bio-rings in the first filter to carry on the filtering in my old tank while my new one cycles.

Sorry if that seems a bit complictated - it seems hard to explain in a more brief way. Thanks for any help.

I have heard of people doing a fishless cycle using shrimp, or prawns. I have a 20 gallon tank, that is about five days old, I have not begun any type of activity in it as of yet. Could someone please let me know how many shrimp I would need to use and how this is accomplished. Do I hang it in the tank with string, is a peice of netting??

I would really like to use this method, can someone help me???

Mario