How to speed up NOB?

[Diego]

Recently I noticed a noticeable level of nitrites (0.25 ppm) lingering in the tank after few days of overfeeding. I have been testing the water daily with the API test kit and never observed any level of ammonia >0. So my theory is that ammonia oxidizing bacteria (AOB) act faster than their relatives nitrite oxidizing bacteria (NOB) so that there will be always an accumulation of nitrite while the excess ammonia is converted to nitrates. Also AOB seems to be generated faster or live longer than NOB. Is this plausible?

Has anyone experience a similar issue? Anyone know how to boost NOB?

The tank is a well established 20 long very heavily planted with gravel-capped dirt substrate. There are 6 white clouds plus lots of cherry shrimps. The excess ammonia is caused by overfeeding. Temperature is around 73F. Two small sponge filters on each side of the tank.

 

[Diego]

Of course the other thing I did not consider is fishfood releasing nitrites directly rather than being broken down to ammonia first. Is that even possible?

[Shadow_Arbor]

36 minutes ago, Diego said:

Recently I noticed a noticeable level of nitrites (0.25 ppm) lingering in the tank after few days of overfeeding. I have been testing the water daily with the API test kit and never observed any level of ammonia >0. So my theory is that ammonia oxidizing bacteria (AOB) act faster than their relatives nitrite oxidizing bacteria (NOB) so that there will be always an accumulation of nitrite while the excess ammonia is converted to nitrates. Also AOB seems to be generated faster or live longer than NOB. Is this plausible?

Has anyone experience a similar issue? Anyone know how to boost NOB?

The tank is a well established 20 long very heavily planted with gravel-capped dirt substrate. There are 6 white clouds plus lots of cherry shrimps. The excess ammonia is caused by overfeeding. Temperature is around 73F. Two small sponge filters on each side of the tank.

 

The issue with your theory is that even if one bacteria "works" faster than the other, their population will increase (or decrease) depending on the amount of food available.

There are a few possible causes to your issue, I will state the two that I believe are most likely and how to counter them.

Theory 1: This, I believe is the more likely case, is incomplete nitrification. This means that the ammonia has been rising and converting into nitrite by the ammonia oxidizing bacteria. For some reason, the nitrite oxidizing bacteria are stressed, this could be as a result of very acidic water, low temp, or maybe a rough filter cleaning. The result? Nitrite oxidizing bacteria reproducing slower, and metabolizing slower. The solution, assuming nothing has changed drastically in the tank recently, water change and check your nitrites, the bacteria will eventually catch up assuming all is in order.

 

Theory 2: Nitrate respiration or incomplete denitrification. Since you have a soil substrate with a cap, I assume you aren't disturbing the substrate. If incomplete denitrification is the cause, it means that the nitrates are being converted into nitrites and then not into their final form of N2 gas. If Nitrate respiration is the cause, it is also a result of different bacteria transforming nitrate into nitrite (a different chemical process than denitrification). The more likely scenario out of the two is Nitrate respiration. Seeing as I'm unsure on how to improve conditions for denitrification your best bet in this case is to reduce nitrates. Less nitrates means less food for the bacteria to turn into nitrite. More info on these topics can be found in Diana Walstad's book Ecology of the Planted Aquarium, specifically page 63.

Edited July 21, 2020 by Shadow_Arbor

[Diego]

Good ideas Shadow_Arbor. I re-read chapter 4 (nitrite accumulation) but I am not convinced. Incomplete nitrification does not make sense. The tank has been established for quite some time and this unbalance is only caused by me adding extra food. Normally there is no accumulation of nitrites, the temperature is fairly constant as the tank sits in my living rom and the ph is high (7.8).

Nitrate respiration could be a thing as the levels of nitrates peaked at 30ppm during the nitirite accumulation event. I have a substrate that would invite anaerobic bacteria but it should effect the tank also when not overfeeding.

The other option is that unlike nitirites which are consumed only via nitrification, ammonia is removed by two processes: nitrification and plants. And plants prefer ammonia/um so they compete against the AOC. If this is true, I should get rid of some biological filtering (sponge filters) and let the plant to take the ammonia instead. Am I over filtering? 

[Shadow_Arbor]

23 minutes ago, Diego said:

Good ideas Shadow_Arbor. I re-read chapter 4 (nitrite accumulation) but I am not convinced. Incomplete nitrification does not make sense. The tank has been established for quite some time and this unbalance is only caused by me adding extra food. Normally there is no accumulation of nitrites, the temperature is fairly constant as the tank sits in my living rom and the ph is high (7.8).

Nitrate respiration could be a thing as the levels of nitrates peaked at 30ppm during the nitirite accumulation event. I have a substrate that would invite anaerobic bacteria but it should effect the tank also when not overfeeding.

The other option is that unlike nitirites which are consumed only via nitrification, ammonia is removed by two processes: nitrification and plants. And plants prefer ammonia/um so they compete against the AOC. If this is true, I should get rid of some biological filtering (sponge filters) and let the plant to take the ammonia instead. Am I over filtering? 

Well if you think about it, incomplete nitrification makes a lot of sense. You over feed your tank, the plants help take up excess ammonia and the ammonia oxidizing bacteria multiply and get to work, now you have a nitrite spike. Seeing as plants prefer ammonium, you're not getting much help from them, so the bacteria are on their own. Assuming more nitrite is being produced than usual, your nitrite oxidizing bacteria need some time to catch up.

 

As for your second point, removing filtration is the worst thing you could do at the moment. Your plants and AOB aren't going to compete with one another in any drastic way. Worst case scenario the plants are taking up all the ammonium and your biological filtration is very weak. Seeing as you have nitrite and nitrate this isn't necessarily the case. Removing filtration will remove all types of bacteria which will only hinder you.

The best thing to do is water change your way out of this situation and next time you decide to over feed do so gradually. Feed a bit more every day until you're feeding the amount you want. That way your mini ecosystem has time to adapt.

[Diego]

Incomplete nitrification makes sense only if you think there is already an imbalance between the AOB and NOB bacterias before overfeeding. Lets say if normally a system can cope with a level x of ammonia as it has enough bacterias (AOB+NOB) to convert it to nitrates, if you increase the level of ammonia to 2x, then you'll will experience a mini cycle: a spike of ammonia followed by a spike of nitrites. So why do I see the spike of nitrites but not the one of ammonia?

I think because the plants are taking in part of the extra ammonia while the AOB population grows, avoiding the ammonia spike. So now a larger population of AOB is producing more nitrites but the NOB population has not caught up yet and plants are not helping there. I register the only spike of nitrites.

Assuming I have enough fast growing plants which could cope with the extra ammonia from the overfeeding, I should not encourage the nitrification via biological filtering which only increases nitrites and nitrates. I think this is the idea behind chapter 7 and the Q&A on page 111 of Diana's book.

Thanks Shadow_Arbor, for the inspiring conversation. I have an experiment to run now. I have already gone through the water changes and yes of course it does work. I'll try something else now: removing a sponge filter. 

 

[ForestJenn]

10 minutes ago, Diego said:

So why do I see the spike of nitrites but not the one of ammonia?

I recently read that the NOB have a slower reproductive rate than the AOB residing in an aquarium, but I'm having a hard time finding that documentation now.  So take that with a grain of salt please.  If this is true though, it could explain what you're seeing.  That by itself would create an imbalance between the AOB and NOB populations.

I'm seeing a similar situation in a very new tank that I kick started with bacteria from other sources.  After adding to the fish population of the tank I noticed an increase in nitrites but didn't see ammonia.  My assumption was that the NOB population needed time to increase and have been doing frequent water changes.   In my case, I have a low pH, so that's not helping either since it appears that NOB are inhibited at lower pH levels.  I consistently see pH test results of 6.8.   That doesn't seem to be your problem.

I enjoyed reading this discussion.  Very informative!  And I can tell you that a google search on this topic turns up a lot of very interesting articles about waste water treatment.

[Shadow_Arbor]

8 hours ago, Diego said:

Incomplete nitrification makes sense only if you think there is already an imbalance between the AOB and NOB bacterias before overfeeding. Lets say if normally a system can cope with a level x of ammonia as it has enough bacterias (AOB+NOB) to convert it to nitrates, if you increase the level of ammonia to 2x, then you'll will experience a mini cycle: a spike of ammonia followed by a spike of nitrites. So why do I see the spike of nitrites but not the one of ammonia?

I think because the plants are taking in part of the extra ammonia while the AOB population grows, avoiding the ammonia spike. So now a larger population of AOB is producing more nitrites but the NOB population has not caught up yet and plants are not helping there. I register the only spike of nitrites.

Assuming I have enough fast growing plants which could cope with the extra ammonia from the overfeeding, I should not encourage the nitrification via biological filtering which only increases nitrites and nitrates. I think this is the idea behind chapter 7 and the Q&A on page 111 of Diana's book.

Thanks Shadow_Arbor, for the inspiring conversation. I have an experiment to run now. I have already gone through the water changes and yes of course it does work. I'll try something else now: removing a sponge filter. 

 

Good luck!

Just want to mention that in theory you could have had a small ammonia spike that you didn't test for in time.

It's also possible that you have many issues at play and not just one. A small ammonia spike, nitrate respiration and incomplete denitrification all working together to bring your nitrites up.