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Thread: Fishless Cycle Questions

  1. #1
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    Question Fishless Cycle Questions

    Good Morning,

    I have some questions regarding the development of Nitrobacter bacteria in my fishless cycle that I can't seem to solve on my own after reading many articles.

    My tank has been cycling for a little over 3 weeks (Started 10/24). I dosed 4ppm pure ammonium chloride with Seachem Stability and Prime following the instructions on the bottle and have seen my Ammonia drop to 0. Nitrites have spiked as well and seem to have started to come down.

    The tank can now handle 4ppm of ammonia in about 12 hours and drop back down to 0. I have reduced dosing to 2ppm. My nitrates were off the charts during the 4ppm dosing and now have dropped to 2ppm. However, this is where my question is.

    My nitrites have stopped going down and have remained at 2ppm for about 3-4 days and my Nitrates remain at 5ppm. I was concerned that perhaps there was too much of the ammonia eating nitrifying bacteria and that it was inhibiting the growth of the nitrobacter bacteria strain and thus slowing my cycle. I stopped dosing ammonia at all for a period of 24 hours to see if this would have any affects and there seems to be no change.

    1. Is there a particular reason why my nitrites and nitrates would remain the same for 3-4 days with no change? I am aware that the Nitrobacter bacteria takes much longer to develop, so is this just me being paranoid and impatient?

    2. Is it necessary to reduce my dosing further or should I still continue to dose 2ppm daily?

    3. Would any other parameters have an affect on this apart from temperature and kH?

    4. I use a gallon box of Marine Pure 1-1/2" spheres and 4 boxtech blocks. Is enough biomedia for 72 gallon planted tank with intert sand?


    Current Water Parameters:
    Ammonia:0 ppm
    Nitrite: 2 ppm
    Nitrates: 5 ppm
    gH: 125 ppm
    kH: 3
    pH: 7.34
    TDS: 250

    Temp: 85F

    The gH is notably high due to there only being 1 water change and the addition of the stones in my aquarium.

    My tank is also planted with anubias and java fern. I dose with Seachem Florish, Iron, Excel, and Potassium on a regimented schedule and I'm seeing pretty substantial growth from both plants.

    *I apologize for the long post, but I wanted to be as thorough as possible. I have ordered 6 fish from Kenny this month and am in the process of planning delivery , but don't want to have them delivered when my tank is not quite ready, (I do have a quarantine tank to hold them if necessary, but no cycled filter media atm hence my concern.)


    Thanks guys

  2. #2
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    Don Speers

    Default Re: Fishless Cycle Questions

    Interesting problem. If your measurements are true then your AOB cycle is complete and your NOB cycle is stalled or completely failed and your Nitrite levels are currently stable due to plant actions rather than a NOB population. Even harder to understand is that you indicate you did see a nitrite surge then rapid conversion to nitrate, indicating an effective NOB population earlier. That is hard to understand unless you possibly did a water change without neutralizing chloramine and your AOB tolerance to cholamine was higher than the NOB, but that would a highly unusual scenario and since I assume you have continued adding Stability even more unlikely. (AOB = ammonia oxidizing bacteria, NOB = nitrite...)

    Couple of observations: I am unaware of AOB ever inhibiting NOB and your biofilter quantity is sufficient or you would not have developed an effective AOB population, although I am curious about your setup, sump? if so what is your flow volume?

    What I would do would be first; verify your nitrites. I am an admitted broken record on this but hate judging colors, hanna does make a freshwater nitrite checker, a little pricey but not compared to 6 Kenny discus. Alternately test some distilled water with your current test to at least verify 0. Also is your test measuring nitrite or nitrite nitrogen and does your nitrite vary with your ammonia dosage since you have gone from 4 to 2 ppm daily.

    If your nitrite value is true then I would try a different source of nitrifying bacteria, e.g. API or Tetra product from LFS if fresh or Chewy. Frankly given that you have fish on the way I might dump both in the tank and at that point go back to the 4 ppm ammonia dosage. As a final thought your nitrifying bacteria use CO2 as their carbon source but can also use organic reduced carbon. I would add a very small dose of high protein flake food daily to promote growth.

  3. #3
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    Default Re: Fishless Cycle Questions

    Hey Don,

    My setup is a 72 gallon display tank with a 30 gallon sump. I have a vectra S2 capable of 1400 gph and that is turned almost all the way up. I have it higher because the plants are still adjusting and there was a tiny bit of die off at first so I'm trying to keep algae at a min and the organic matter I couldn't remove by hand stirred up into the water column so I can be removed by the overflow.

    I saw a Nitrite surge but have never seen more than 10 ppm of Nitrates. They dropped to 5ppm with a 50% water change I had to do to prevent a pH crash. (I have very soft water and my kH had been almost entired depleted by the cycle). I redosed prime and stability after this water change and slowly correcty the kH problem over 3 days to bring it back up to 3.

    I will test my tap water again but the first time I did it didn't have any nitrites/nitrates or ammonia but it's worth testing again. My nitrite didn't vary dramatically after reducing my dosage. I do know they were higher than they are now but I can't tell them reducing is due to the dosage or cycle conversion due to them dropping by such a small amount.

  4. #4
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    Default Re: Fishless Cycle Questions

    Also tested my tap again.

    Ammonia: 0ppm
    Nitrite: 0ppm
    Nitrate: 0ppm
    pH:6.8
    kH:2
    gH:3
    TDS:33

  5. #5
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    Default Re: Fishless Cycle Questions

    One sure way to note whether or not you tank is completely cycled is if you see algae on the class. Usually a brownish hue.

  6. #6
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    Default Re: Fishless Cycle Questions

    I do have algae growing on the glass and the rocks, in small amounts there are also copepods that are there eating it. I usually clean the glass before it gets bad. I'm just confused as to why my nitrites arent dropping. But I think it just might need more time, I'm only in my 3rd week.

    Probably just going to wait to receive fish until after Thanksgiving.

  7. #7
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    Default Re: Fishless Cycle Questions

    That's some amazing water. I am with you in being confused in re why the nitrites have stalled especially given that they peaked and then fell to current values. Out of an abundance of caution I would still add a different brand of nitrifying bacteria, certainly cannot hurt. Only place the nitrates can go is into the plants unless you somehow also established an anoxic denitrifying colony which is almost impossible on this time line if you even accept the premise that it can be done on a small aquarium scale. Given that your plants are thriving and not showing signs of nitrogen deficiency, I am convinced that they are keeping up with nitrate production. Hopefully time will fix.

    Just out of curiosity why such a low kH? usual recommendation is minimum of 5 unless breeding.

  8. #8
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    Default Re: Fishless Cycle Questions

    My kH is just naturally that low. I do plan on running it around 5 but didn’t want to do too many changes during this cycle until I figure out what it’s doing.

    I’m thinking that it might just be a little too early still to be making major changes to water chemistry.

    Do you have a suggestion for types of bottled bacteria? I’ve tried to do more research on this topic but there isn’t really a definite answer here.

  9. #9
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    Default Re: Fishless Cycle Questions

    Do you think doing a water change to help lower my nitrites would help at this point? My test for them is still coming up bright purple and it hasn’t changed for over a week. Nitrates remain the same.

  10. #10
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    Default Re: Fishless Cycle Questions

    ATM products look interesting though I have not used, I would order directly and skip amazon as you never know what has happened to the bottle between the manufacturer and storage. I have access to seasoned filter material from a trusted source so do not have to deal with this. The issue is always whether the bacteria in any given bottle is still alive.

  11. #11
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    Default Re: Fishless Cycle Questions

    what kit are you using? bright purple sounds like a lot more than 2ppm. I hate colors, I use Hanna checkers (except when I can't like nitrates). I am unaware of a level of nitrite that is toxic either to plants or nitrifying bacteria, so doing a water change to lower nitrites should not be necessary.

  12. #12
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    Default Re: Fishless Cycle Questions

    I've been using API master test kit and the expiration date isn't until 2025, I went ahead and purchased Salifert test because I'm not sure it's accurate.I performed a 50% water change without disturbing the substrate and tested again and I think something must be wrong with the nitrite test because nitrites read exactly the same thing. Still bright purple. I don't understand how this is possible after a 50% water change.

    I was reading some of Dr. Tim's (Dr. Tim's Aquatics) articles on the fishless cycle. Normally I read more than one source but he does have a PHD in Ecology, Evolution and Marine Biology so i figured maybe what he has to say is somewhat reputable.

    According to that article:

    Many times the bacteria can quickly handle the overdosing of ammonia and you will get a zero (0) ammonia reading but the nitrite just gets higher and higher. High nitrite is very common when you rush the process or add too much ammonia too quickly. High nitrite inhibits the bacteria and stalls the cycle. If you have super high nitrite do a 33-50% water change without disturbing the substrate. Do not add chemicals to de-toxify the nitrite.

    Well see if this helps.

  13. #13
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    Default Re: Fishless Cycle Questions

    I recommend you take a water sample to your local fish store. They'll do a free analysis for you. Because they get a lot of requests, their chemicals are always fresh. Whether or not your results make sense, it's always good to get an outside benchmark.
    At my age, everything is irritating.

  14. #14
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    Default Re: Fishless Cycle Questions

    On the API unless I am reading wrong the bright purple is max or 5+ ppm meaning the value could be 5 or could be 20 or 60 so diluting by half with a water change would still give a value of 5+. Dilute your sample serially 1:1 (with distilled water) and retest till you get a value less than 5. 1 dilution multiply the value by 2 for the correct concentration: 2nd dilution multiply x 4: 3rd x 8: etc, My understanding is that if you keep your nitrites below 20 ppm you should not stall development of your NOB (my statement above was in reference to the values you were reporting, my understanding is that very high levels of nitrite can be toxic to your NOB but more to your AOB and generally at a pH < 6.0). Frankly given your very low kH, surprised your pH didn't bottom out. Confirming your values as Willie recommended is always a good idea. Do not completely stop adding ammonia to sustain your AOB but I would limit to 1ppm/24 hours till nitrites start to fall, remember 1ppm ammonia converts to approx 2.7 ppm nitrite. What temp are you maintaining the tank at?

  15. #15
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    Default Re: Fishless Cycle Questions

    That would make since and explain why I keep getting the same result with my test kit since it only goes to 5ppm. My pH did start to bottom out but I raised my kH to compensate and keep it going below 6. I run an apex controller on my tank so I am able to track pH swings in real time. It stays between 7.1-7.3 now. My tank is consistently 85+/- .1 degree.

    If my math is correct it seems like after a x3 serial dilution I got a reading of 1ppm so I have 8ppm of nitrites.
    Last edited by Bradb90; 11-17-2020 at 04:01 AM.

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