Aquarium Cycling Without Killing Your Fish

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.

Tell us about your cycling story.

, , , , , ,

71 Responses to Aquarium Cycling Without Killing Your Fish

  1. Fish Lover October 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 October 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 November 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 November 26, 2007 at 9:38 pm #

    Hi Regina, Glad you enjoyed!

  5. adge December 9, 2007 at 7:31 am #

    can you have to much filteration in your tank

  6. Eric December 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 December 19, 2007 at 10:52 am #

    eric thanks for your info appreciated

  8. adge December 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 December 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 January 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 January 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 January 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 January 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 January 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 February 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.
    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 February 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 February 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 February 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 February 24, 2008 at 2:57 pm #

    Hi David,

    Take a look here.

  20. Josh March 3, 2008 at 2:40 pm #


    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 March 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 March 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 March 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 March 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.

  25. Eric March 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 March 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 March 10, 2008 at 7:57 pm #


    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.

  28. anon March 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 March 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 March 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 March 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 March 20, 2008 at 8:23 pm #

    Hi NT,
    Take a look here.
    Basically you use bacteria starter and introduce your fish very slowly, 1-2 a week or so.

  33. Eric March 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 March 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 April 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 April 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 April 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 April 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 April 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 April 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 April 23, 2008 at 9:28 pm #

    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 April 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

  43. Stanley May 29, 2008 at 10:34 pm #

    As long as you keep the chemical balance proper, there is no need to delay adding fish. I wouldn’t fully stock a tank the day it’s set up, but unless you are stocking with sensitive fish, i.e. discus or many reef dwellers, it shouldn’t be a problem. You are making this into a big deal when it isn’t. As for the comment closer to the top about a fish bowl, and how careless it was for the store owner to send home fish with the bowl– goldfish are extremely hardy, and the presence of “beneficial bacteria” in a fishbowl is dependent on the presence of fish. Leaving a bowl of water sitting on a shelf won’t breed healthy fish water.

  44. Katie June 2, 2008 at 8:33 am #

    I have read the articals on cycling, and do understand the whole ammonia-nitrogen cycle. I have started a tank 3 weeks ago, all my levels, pH, nitrite, nitrate and ammonia are in range.
    But the fish continue to die, is it still too young of a tank?
    The water is clear, no food on the bottom, we thought maybe we were over feeding, (originally someone told us 2 times a day) now we are down to 1 a day. Any suggestions?

  45. Eric June 3, 2008 at 8:04 pm #

    Hey Stanley,
    You make a great point about fish being necessary to actually grow bacteria. I would like to make sure everyone understands that. It’s the waste that actually kicks off the bacteria growth. The problem is too much, too fast. Many times hardy fish will survive cycling but the can also suffer from the stress. The key is adding new fish at slow rate.

  46. Eric June 3, 2008 at 8:10 pm #

    Hello Katie,
    The young tank is only a problem if it causes your ammonia, nitrates, & nitrites to shoot up. Look for signs of disease. Temperature OK? Any bullying going on?

  47. katie June 4, 2008 at 6:18 pm #

    Hi Eric,
    Well it sure is a puzzle, the levels seem fine. We had one day where the pH was 8.6, that was after a death. No signs of disease, temp runs at 80, no bullies.

    Since we started the tank on Mothers day weekend, we have lost 2 albino cats, 1 ghost cat, 2 guarmies, 2 angel fish, 1 platy, a fancy guppy, and 4 black tail somethings i dont know the name of …
    Mind you, these were not all in the tank at one time… usually just replacements from others that died, we decided to just wait now a few weeks to see if we loose more.
    I really love the tank, and i feel so bad when they die 🙁 Like I failed the poor guys.
    I just wish there were a clear cut answer.

  48. Eric June 8, 2008 at 2:35 pm #

    Yeah, I think slowing the replacements down is a good idea till you get it figured out. 8.6 is a very high pH level for a freshwater tank. That could be enough too be your cause.

    Before adding any more of the more sensitive fish it would be a good idea to start with hardier fish. Zebra Danios are some the most tolerant. After success with those, you could then start adding others.

  49. Vince June 11, 2008 at 3:50 am #

    first of all, amazing article. its a shame that local pet shops wont even help you out on this subject.

    but on to my question. I have a five gallon tank with a few fish, and its equiped with a bio wheel filtration system. i’m “upgrading” to a ten gallon tank and have purchased an appropriate filter with a bio filter. now is it a good idea to take my old biowheel and just float it in my new tank for a day or so to get it going? because i’m simply moving up in tank size and moving my fish, i’m unsure. common sense is telling me to utilize some of the water from the old tank and to put some of the old gravel in the new tank. any help would be nice.

  50. Eric June 14, 2008 at 10:01 pm #

    Hi there Vince,

    Thanks for the kind words. You are spot on. Floating the bio-wheel, transferring your old gravel without cleaning it, and using the tank water all help move your bio filter rather than re-building from scratch. That is exactly what I suggest.

  51. Chris June 15, 2008 at 10:51 pm #

    Hello Eric,
    very nice & informative site you have here…..i have a question about tank cleaning….i’m about to inherit an 80 gallon that was used as a saltwater tank…i want to use it as a freshwater setup…are there any certain cleaners/chemicals that i should use or not use in the cleaning process???….i dont want to use anything that may linger & cause trouble later…i’m sure i’ll have filter ?s & stuff later after i see exactly whats coming with this setup……thanks

  52. Eric June 17, 2008 at 5:52 am #

    Hi Chris,
    Plain water is your best bet. Steer clear of soap or cleaners completely. Bleach can be used for HARD plastic/glass parts in VERY low concentrations but I don’t suggest it. Even trace amounts left around can kill your fish. Water and some hard work will usually get the job done.

  53. Lawrence July 8, 2008 at 2:43 pm #


    I love your site and the question and answers have been great.

    I have a a new 55 gallon column tank. I’m using an Aqua Clear Power Filtration 70 system. I have stone aerator under my gravel centered in the tank. I have added conditioner, water treatment and some rock crystals that dissolved on the gravel.I’m at day 2 since adding my water and running the system.

    My question is:


    1. When should I add the hearty type of fish to begin the cycling process? I have read and do understand the best type of fish to start off with.

    2. When should test the water before any fish are added or after?

  54. Eric July 10, 2008 at 6:17 am #

    You should give it a week or so before adding your first fish. A tank that size is a little more forgiving so you can start with few if your going with small fish like Zebras. If you are using larger fish, just start with one.
    You can test before you add fish for PH, GH, KH and such but you don’t need test until after you add fish for ammonia, nitrites & nitrates. These levels only increase after you add fish (which make waste) to the tank.

  55. Brooke July 23, 2008 at 7:42 am #

    Hi there, great article! How would oscars and catfish go with the cycling process? Atm, I’ve filled the tank with water 4 days ago, put in all the chemical-bacteria as suggested, ph and water temp are ok. Would it be safe to add my oscar?

  56. Brooke July 23, 2008 at 7:47 am #

    Sorry I perhaps should have also mentioned that I’m running an underwater gravel filter which stretches the length of my 4 foot tank, as well as another large filter.

    Woudl there be any problem to add 2 oscars, providing that I kept a close eye on the nitrate and ammonia levels and did regular (i.e. every 1-2 days) water changes for the first 4 weeks?

  57. Eric July 25, 2008 at 6:18 am #

    Hey Brooke,
    Oscars and Cory Cat’s are both hardy fish. Sounds like it’s about time to add your first fish. You would be better off starting with one but if you have a couple small Oscars and big tank, two would be fine. During the first weeks of the cycling process, you’ll want to test daily as you make decisions on when to add more.

  58. Scott July 26, 2008 at 9:27 pm #

    Eric, I’m one day into cycling up a new 120 litre tank. Using a Nutrafin Master test Kit, first results are pH >7.6 (low range test kit), GH 80ppm, KH 50 ppm, Nitrite <0.1 ppm, Ammonia <0.6ppm. Water temp is 25 degC. I am aiming for neutral pH of 7.0, Nitrite and Ammonia obviously 0, GH 100-140ppm, KM 80-105ppm and maintaining temp @ 25degC. Are the GH/KH targets OK?? Prefered species (eventually) would include cherry barb, neon tetra, angle fish, silver shark and bristle-nosed catfish.

  59. Eric July 28, 2008 at 6:13 am #

    Hey Scott,
    Take a look here for some info on hardness.
    The cycling process is all about controlling Ammonia, Nitrites, and Nitrates. The others can of course be altered but it takes other methods. Your pH is a bit on the high side. This post and the comments have a bunch of info on adjusting pH.

  60. Brooke August 1, 2008 at 6:49 am #

    Well we’re up to day 7 with my oscars and catfish in the tank and we’re going as expected. Being a newly set up tank, the ammonia is hitting 4.0ppm so doing daily water changes of 25% and adding good bacteria as well as some stuff to combat the ammonia/ nitrite- fish are happy, but perhaps a little too happy???…

    I have two oscars in the tank, which NEVER leave each other side and want to be touching each other all the time. They swim together, sleep together, eat together – is this behaviour of a breeding pair? I was of the impression that oscars are independant fish and go about their own buainess, so I”m finding this behaviour a little odd. They’re about 12 months old, possibly a ripe age for spawning although I thought this was usually only after 18 months. Anyone know whether this is the type of behaviour breeding oscars will do?


  61. Tom H August 1, 2008 at 1:00 pm #

    Hi Eric,

    I apologise if I’ve not found the relevant info on this, and you end up repeating links over and over to me!

    I bought an 80 litre tank, set it up with plants then left it a week to stabilise. Then, when the water had cleared and the litmus type paper tests looked ok I added 6 tiger barbs. These seemed to get on fine straight away so the following week (a week ago) I bought two bristlenose Plecostomus to feed on the increasing quantity of algae. My local aquarium supplier suggested these as a good choice because they are a hardy species that doesn’t grow that large (unlike some!).

    The problem is that in the space of a week both fish have died. Their scales were coated with a fine layer of what I can only describe as white slime(!). The temperature was slightly higher than I wanted due to the recent warm spell but regular water changes (about 10%) helped to keep that (and the levels of nitrate/nitrite etc) within acceptable levels. Let me know if you need more accurate pH and nitrite/nitrate levels, I can do a quick check.

    Sorry for long question!

    Hope you can help,


  62. Eric August 6, 2008 at 6:17 am #

    This is the typical behavior of Oscars pairing off. There is no way to really tell until you see more. It would be odd for any breeding to go on in your tank already though. Generally fish need to have have good conditions and be comfortable with their surroundings.

  63. Fish Enthusiast August 6, 2008 at 12:31 pm #

    Thanks for the nicely written article. You might want to add additional information to step 1. In order for the bacteria to grow whether naturally or via Bio Spira or Seachem Stability, etc., you will need a source of ammonia. Without the ammonia, the bacteria will starve and die off before it gets a chance to mature and populate. I know Bio Spira ships the ammonia within its product, but it still needs a constant supply of ammonia. That is why the makers of Bio Spira recommend you add fish within days of adding their product…simply because fish will give off that needed ammonia to grow the bacteria culture on the surfaces of the tank. Aside from that, good article!

  64. Eric August 10, 2008 at 9:12 pm #

    Hello Tom H,
    Bristlenose Plecos are great algae eaters for smaller tanks! From what you describe, you might have been dealing with a fungus. I wouldn’t generally describe a fungus as a slime but rather sort of white cotton like patches. Ich also come to mind but usually looks like white salt like specks. Take a look here for Ich suggestions if that descriptions fits . If it was a fungus, you can also find treatments at your local fish shop. Methylene Blue is one that comes to mind.

    Here’s what I suggest though. If you don’t see signs on any other fish, I would leave it alone and just keep a close eye on things. If your testing levels are in order, you shouldn’t have to deal with much unless you bring your fish home infected that way. That’s where a quarantine tank comes in handy.

  65. Eric August 10, 2008 at 9:18 pm #

    Hey there Fish Enthusiast,
    Thanks for the input! I may even write a separate article around your point to make sure everyone understands the relationship. It’s discussed in some comments but probably not well enough. You’re right on target! Thanks for noticing what would help everyone.

  66. Bob Lintault October 6, 2008 at 12:18 pm #

    I have a 47 gallon tank and recently lost all of hte fish I had in it because I simply added too many too soon. After that I started all over again and and did not any fish for several (3) weeks. however, the ammonia levels have continued to be oof the charts with very acidic (low Ph) water. I can’t seem to get hte ammonia down or the Ph up. I have added two South American fish that are doing Ok in spite of the ammonia levels. I have two filter systems, lots of aeration, and three tubes pulling the water from the bottom filter plate. Plus i have lots of plants. Why isn’t the ammonia going down and the Ph going up? It has bee 6 weeks now.

  67. Eric October 7, 2008 at 6:00 am #

    Hi there Bob,
    The key to dropping that Ammonia quickly is to dilute it with water changes. You really want to get it to a reasonable level that isn’t stressing your fish. I suggest 50% changes every few days for a week or so. You should be able to get it to an unmeasurable level. Keep 25% changes up weekly after that. You can then increase or decrease those changes, checking Ammonia regularly, as needed. Grab some bacteria starter to add each time you do water changes. That will help kick start the good bacteria. The problem is that your tank can’t naturally get rid of the ammonia yet until your bio-filter is established.
    Take a look here for some pH tips. It’s very likely that your pH will stabilize with those water changes and once you get your Ammonia in good shape.

  68. Jeffrey Mart November 18, 2008 at 5:30 pm #

    How frequently do you think I should check the water conditions during this process?

  69. Eric November 18, 2008 at 7:26 pm #

    Hey Jeffrey,
    When you first start adding fish early in the process you should be checking every couple of days. If everything looks to be in good shape after a week or so of that, you can start spacing them out more. Every 3,4,5 days, etc. It’s a good habit to get in to checking your water once a week after things stabilize.

  70. Kerrie Madge November 22, 2011 at 11:28 am #

    Ok so I have recently purchased a used 70 gal tank and using the old filter that came with it to help build up the bacteria. The pet store in my town seems to know NOTHING as I have bought 45 gold fish there in the last 2 weeks and I have 7 left (not all were in there at the same time). I have religiously checked my levels and they are all what I seem to believe as in normal range I have discovered last night that they have ich and I am thinking that I will NOT be able to save them in time. I fell terrible about this whole process and just want to get this going right and stop killing all the fist.

    The guy at the store here says you need to cycle your tank, now I had a 20 gal before and as for their signs of cycling (cloudy of green water) after 3 years it never cycled, he also suggests that the only fish that you can buy are gold fish (feeder) because everything else will die. I am not sure what to believe with him and would love to hear some feed back on how to start my aquarium again after I treat for ich, which fish are safe to start with how many for the 70 gal size etc. Please really hoping for a quick response and some answers

  71. Eric November 27, 2011 at 9:26 pm #

    Hi Kerri,
    So sorry for the slow reply. I’ll try and answer everything you are asking.

    The reason they suggest feeder goldfish is because they are pretty hardy fish and of course cheap. There are plenty of other hardy fish that you can start with. I usually suggest something like Zebra Danio’s.

    I can say this. There is a better way than to just expect them to die. The key is the quantity you add. You should really start with a smaller number of fish even though you have a big tank. Maybe 5 fish to start.

    My thoughts on your fish dying though is the Ich. You see, if you are having trouble cycling your tank you’ll see the ammonia/nitrate/nitrite levels spike. If you aren’t seeing that, then the cycling isn’t what’s killing your fish.

    I would try some fish from another outlet and start with fewer once you get rid of the Ich.

    There are a lot of tips about ridding your tank of Ich in the post and comments here: