Looking for some assistance with really basic nitrogen cycle question.

[rocknut]

So I have had a reef tank in one form or another for about 10 years, and have had some form of an aquarium for about 20 years. With that in mind, I'm not too proud to admit when I feel like I missed really basic piece of knowledge during Reefing 101. I have had really successful tanks, and some disasters, but can't honestly say that I understand why some have worked, and some haven't worked. Trying to eliminate so much guess work.

Feel free to explain this to me like I'm a five year old, because I just want to really understand this concept. First some background: I re-booted my current 150 gallon reef tank in April 2016 (so 18 months) and had planned to run this in a more "old school" style and go with a good skimmer, lots of good quality live rock, 2 part dosing, strong flow, strong light, etc. So, I have had good luck keeping the Big Three (Alk, CA, Mg) is good balance, and fairly steady. I have had lots of problems with the balance of my nutrients, however, and there in lies my need for some explanation and clarification. I have had more or less zero phosphates since about three months in to the tanks life. I check with the Hanna ULR Phosphorus checker, and judge based on how often I need to clean the tanks glass. Along with the undetectable phosphates, I have always had elevated levels of Nitrate, especially considering that my bio load is fairly small (has been three fish) for a 150 gallon tank. I have been carbon dosing since last August, and have had pretty mixed results. Seems like the tank fluctuates between starving, and barely growing as my phosphates are either totally zeroed out, and I'm not cleaning my glass for two weeks, or barely detectable (like 3-4 ppb). Recently my Nitrates pushed up to between 16-32, so I performed five bid 25% water changes of the course of two weeks, and pushed them down to 4. Two weeks later they are back to 8, with PO4 being undetectable the whole time.

It has been suggested by several people that I know to be quite knowledable, that somehow my system is not denitrifying like it should be. It has also been suggested that I don't have enough fish, and that by adding more fish, and basically doubling my feeding, I could basically boost up the denitrifying bacteria in the tank. At first, this seemed really counter intuitive: wouldn't I just add even more nitrate by adding more fish/more feeding? However, the more I thought about it, I feel like maybe this has been the missing link for me. Would more fish producing more waste, create more ammonia, and in turn boost the bacteria that eat nitrite, and finally allow more denitrifying bacteria to grow in the tank? In turn, more fish would maybe get some phosphates to show up which could balance out, and lower the nitrate levels? Because I have always kept such a small bioload, have I been stunting the tank denitrifying capability? Again, I could just take this advice and add more fish, but I really want to understand what is happening, not just follow a recipe with no real idea of why it works, or doesn't work.

I have always known plenty of people that run reefs with "undetectable" NO3 & is PO4, with nothing more than live rock, and a skimmer for filtration, and have been totally confused (as I hook up my biopellets, etc). They do always have a higher bioload as well. Again, just feel like my tanks have been hobbled by a gap in my knowledge, so really want to understand this.

Thanks in advance for reading this, and responding.

 

[Randy Holmes-Farley Verified Community Expert]

Can you describe any filtration/nutrient export methods you use?

Adding ammonia won't help denitrification, but adding phosphate might since it could be limiting the process and especially if you are carbon dosing and still have a lot of nitrate.

That said, how confident are you in the nitrate kit result? Does it read zero on new salt water?

 

[rocknut]

Can you describe any filtration/nutrient export methods you use?

Adding ammonia won't help denitrification, but adding phosphate might since it could be limiting the process and especially if you are carbon dosing and still have a lot of nitrate.

That said, how confident are you in the nitrate kit result? Does it read zero on new salt water?

Hello Randy,

I am using a 30" Lifereef Venturi skimmer in the sump, I also use filter socks that are changed out every two days, plus my live rock (about 100 pounds of aquacultured live rock). I run some GAC, passively in a media bag, but am setting up a reactor for this in the next few weeks. I have been running a small amount of NoPoX for about a year, and using a total dose of about 2-3ml/day total was allowing my phosphates to stay at about 5-6 ppb, but even at 1ml/day, I can't get them up from undetectable at this point. That's about it.

I think my nitrate kit is good? It's the Red Sea Pro kit, and I just bought some reagent refills about a month ago. I haven't tested any new salt water in awhile, but it was undetectable when I last checked, but could definitely test again.

I have been dosing some Brightwell NeoPhos for the last two weeks (about 5ml/day) but still can't get a detectable reading on my Hanna Phosphorus checker (with brand new reagents). That seems to be correct because I have zero algae growing in the tank, and can go over a week before I need to clean the glass on the tank.

Honestly, this whole conversation started after I was e-mailing with a vendor regarding buying an algae reactor. He suggested that I add some fish to boost the denitrifying bacteria in the tank, and got some phosphate into the water before I would think about trying to grow any Chaeto in the tank.

So I have always been under the impression that by adding "X" amount of live rock, you get a basically fixed amount of denitrifying bacteria. I have chosen to keep a small bioload thinking I could more or less have more denitrifying bacteria than I need, and thus keep the nitrates low. What I started considering is that by having a low bioload am I just decreasing the amount of denitrifying bacteria because their population is proportionately linked to amount of waste being introduced to the tank? So by increasing the bioload, and producing more waste, am I increasing the entire chain of bacteria so that I have more denitrifying bacteria as an end result? This absolutely may not be correct, like I said, I'm just trying to get a better understanding of this whole concept.

 

[Martin Kuhn]

Hello rocknut

From what I read, this might be either an issue with suboptimal flow OR you could solve it with adding and feeding the proper bacteria species

Could you post images of your tank where we can see type/positions of your flow pumps ?

 

[CNDReef]

I do agree that the bacteria is proportional to the load, but I don't think it wouldn't handle the waste of 3 fishes in a 150. I don't dose nopox but dose vodka, I have a 29 gallon tank and my daily dose is 2.5 ml just to keep my nitrates down to 10. You might need to up your dose a little

 

[Brew12]

Adding ammonia won't help denitrification, but adding phosphate might since it could be limiting the process and especially if you are carbon dosing and still have a lot of nitrate.

Completely agree with this. The nitrogen cycle from ammonia to nitrite to nitrate is all done by aerobic bacteria. Denitrification, the process of turning nitrate into nitrogen gas, only happens in anaerobic zones. This can be deep within live rock or other dense porous materials in no/low flow areas or in deep sand beds. If you have any NO3 in your system, you will develop denitrifying bacteria in these areas. Adding more NO3 to the system is like adding more food to an already well stocked buffet. It won't make people eat more if what they want is already available.

For most reefers, anaerobic denitrification via bacteria just isn't practical. That means we need to resort to other methods of nitrate removal. What almost all of them have in common is the need to grow bacteria and/or algae to consume the NO3. To grow and reproduce, both algae and bacteria need PO4. If your system is PO4 limited it can reduce the effectiveness of traditional NO3 removal methods. You may even find that if you add an algae reactor but are PO4 limited the algae will just die off instead of growing.

 

[rocknut]

Hello rocknut

From what I read, this might be either an issue with suboptimal flow OR you could solve it with adding and feeding the proper bacteria species

Could you post images of your tank where we can see type/positions of your flow pumps ?

Hello Martin,

I am running three Neptune WAV pumps, and a Tunze Wavebox. I took a video of my tank, and I will *try* to post it here: If that doesn't work, I think that the flow in the tank is pretty good, as I don't really have any dead spots in the tank, and the flow is pretty random. I have two WAV pumps on the left side wall, facing one WAV pump, and the Wavebox on the opposite side.

Let me know what you suggest regarding bacteria additions?

 

[rocknut]

I do agree that the bacteria is proportional to the load, but I don't think it wouldn't handle the waste of 3 fishes in a 150. I don't dose nopox but dose vodka, I have a 29 gallon tank and my daily dose is 2.5 ml just to keep my nitrates down to 10. You might need to up your dose a little

Thanks for the input. I have definitely gone back and forth on this...Seems that if I increase the dosage of NoPoX, I strip the tank completely of PO4 and have issues with the corals, and a build up of slime. Too little and the NO3 sneaks up?
Honestly, I just read through an entire thread from an Australian SPS keeper that only runs a skimmer, and then does 25% water changes each week, and has one of the most beautiful tanks I've ever seen. Kind of food for thought. I don't mind doing more water changes if it could drastically simplify things.

 

[rocknut]

Completely agree with this. The nitrogen cycle from ammonia to nitrite to nitrate is all done by aerobic bacteria. Denitrification, the process of turning nitrate into nitrogen gas, only happens in anaerobic zones. This can be deep within live rock or other dense porous materials in no/low flow areas or in deep sand beds. If you have any NO3 in your system, you will develop denitrifying bacteria in these areas. Adding more NO3 to the system is like adding more food to an already well stocked buffet. It won't make people eat more if what they want is already available.

For most reefers, anaerobic denitrification via bacteria just isn't practical. That means we need to resort to other methods of nitrate removal. What almost all of them have in common is the need to grow bacteria and/or algae to consume the NO3. To grow and reproduce, both algae and bacteria need PO4. If your system is PO4 limited it can reduce the effectiveness of traditional NO3 removal methods. You may even find that if you add an algae reactor but are PO4 limited the algae will just die off instead of growing.

Thanks for this, Brew12. That is why I'm here: want to really learn what is really going on in the tank. After 10 years of reefing with some success, and a healthy portion of failure, I have had to come to the realization that it has been a larger percentage of luck in finding some balance of equipment, fish, additives, bioload, etc that has worked (or not worked). Ultimately, I would just like to understand these basics better, and your post is good info.

So, I follow your logic that I really should have plenty of area available for denitrification in the tank. If you watch my video, I have quite a bit of live rock, some sand, etc. So, knowing what I know about the Redfield Ratio (which is admittedly just a surface knowledge) it would make sense that my tank is truly deficient in phosphate. My three fish are just not adding enough PO4 to the tank to allow the NO3 to be processed? My thought was that increasing the bioload, and not necessarily over feeding, but just adding a few more fish would help balance this out? I did add a trio of Anthias yesterday, but with six fish, still think my tank is on the lean side of bioload for the tank size. I am going to hook up my bottle Brightwell NeoPhos to my doser today, and watch my levels CAREFULLY and see if this does the trick...

 

[Lasse]

About denitrification and its demands

with adding more food/fishes - you will rise your nitritate levels for sure. you will also rise your organic matter but if you do not have any proper anaerobic area and fast organic carbon source - you will not have any denitrification.

I totaly agree with Brew12 and Randy Holmes Farley

With help of adding phosphates and some fast organic carbon you will help the bacterial process named DNRA (dissimilatory nitrate reduction to ammonium). How could this help? Ammonium (ammonia ion NH4) will normally turn to nitrate again - yes - some of it but some will leave the water through the gas exchange in the skimmer (as ammonia gas, ammoniac, NH3)

NH4/NH3 is a complex there the percentage of each compound depends on pH. At a pH just over 8 – 25 degree C – the NH4 part is around 94 % and the NH3 part around 6 %. NH3 is a gas and will be removed through gas exchange in the skimmer. When some NH3 is removed a new equilibrium will take place through some of the NH4 will be transferred to NH3 following the same percentage.

At pH 7.5, 25 degrees C – the ratio is around 98/2 (NH4/NH3) - At pH 8.5, 25 degrees C - the ratio is around 85/15. It means that it is easier to aerate out NH3 at a higher pH (and in fact also at higher temperatures)

IMO – this is the most important bacterial/chemical nitrogen removing pathway in many (heavy) skimmed tanks without DSB or other denitrification constructions.

Microalgae, Macro algae and zooxanthella is good biological nitrogen removing pathways but even here – you need phosphorus and nitrogen to be in a certain ratio. For macro – this ratio can be very high in favour to nitrogen, they are effective to take up nitrogen



Sincerely Lasse

 

[rocknut]

About denitrification and its demands

with adding more food/fishes - you will rise your nitritate levels for sure. you will also rise your organic matter but if you do not have any proper anaerobic area and fast organic carbon source - you will not have any denitrification.

I totaly agree with Brew12 and Randy Holmes Farley

With help of adding phosphates and some fast organic carbon you will help the bacterial process named DNRA (dissimilatory nitrate reduction to ammonium). How could this help? Ammonium (ammonia ion NH4) will normally turn to nitrate again - yes - some of it but some will leave the water through the gas exchange in the skimmer (as ammonia gas, ammoniac, NH3)

NH4/NH3 is a complex there the percentage of each compound depends on pH. At a pH just over 8 – 25 degree C – the NH4 part is around 94 % and the NH3 part around 6 %. NH3 is a gas and will be removed through gas exchange in the skimmer. When some NH3 is removed a new equilibrium will take place through some of the NH4 will be transferred to NH3 following the same percentage.

At pH 7.5, 25 degrees C – the ratio is around 98/2 (NH4/NH3) - At pH 8.5, 25 degrees C - the ratio is around 85/15. It means that it is easier to aerate out NH3 at a higher pH (and in fact also at higher temperatures)

IMO – this is the most important bacterial/chemical nitrogen removing pathway in many (heavy) skimmed tanks without DSB or other denitrification constructions.

Microalgae, Macro algae and zooxanthella is good biological nitrogen removing pathways but even here – you need phosphorus and nitrogen to be in a certain ratio. For macro – this ratio can be very high in favour to nitrogen, they are effective to take up nitrogen



Sincerely Lasse

@Lasse Thanks so much for this info. I've read through it about ten times, and wanted to ask you a few questions:

Quote: "with adding more food/fishes - you will rise your nitritate levels for sure. you will also rise your organic matter but if you do not have any proper anaerobic area and fast organic carbon source - you will not have any denitrification."

Okay, so could I assume that by having a good amount of live rock, I do in fact have the proper area for denitrification to occur? So the fish/food will add organics and produce phosphates (as well as nitrates), but if I don't have enough phosphates, or a sufficient amount of carbon in the system, any real denitrification can't occur and the nitrates aren't processed out, and they build up? I'm assuming that with any fish in the system, phosphates are being produced, but maybe not enough in comparison to the nitrates, which doesn't allow the denitrification process to fully take place? Sorry if I'm being slow - I don't want to be too proud and not ask questions.

Quote: "With help of adding phosphates and some fast organic carbon you will help the bacterial process named DNRA (dissimilatory nitrate reduction to ammonium). How could this help? Ammonium (ammonia ion NH4) will normally turn to nitrate again - yes - some of it but some will leave the water through the gas exchange in the skimmer (as ammonia gas, ammoniac, NH3)"

So moving forward with dosing a Phosphorus additive + a carbon source (Red Sea NoPoX in my case) is the best way to go, it seems. Here is my next question: any theories on how my system evolved into its current state, being so deficient in Phosphates? Seems like typically reef systems have no/low nitrates, but fight to keep phosphates down. Any ideas on how mine might have gotten reversed?

Also, by continuing to add a carbon source, and now adding Phosphorus as an additive, will my system eventually become more "balanced" so that I will have phosphate and nitrates in a more natural balance? That is what my original plan was, I guess: add some more fish to get more organics/phosphates into the system, knowing that this would of course also add nitrates, but by being ready to do some large water changes each week to keep the nitrates from climbing too high. I was reasoning that eventually the increased phosphates would be elevated enough to allow them to balance with the nitrates in a more natural ratio so more denitrification could occur? I understand that adding just phosphate to the water makes more sense, because you are not elevating nitrates at the same time, but do you think my original plan would have eventually gotten me to the same place? Albeit with MUCH more water changes.

Again, thanks so much for this information. I really appreciate it. I have also enjoyed starting to read your build thread this evening.

 

[mcarroll]

Along with the undetectable phosphates, I have always had elevated levels of Nitrate, especially considering that my bio load is fairly small (has been three fish) for a 150 gallon tank. I have been carbon dosing since last August, and have had pretty mixed results.

Some folks hit on it already, just piling on......phosphates being unavailable is holding things back in your tank.

I am going to hook up my bottle Brightwell NeoPhos to my doser today, and watch my levels CAREFULLY and see if this does the trick...

Watch that you don't drive N levels to zero in the process. Zero nitrates are not as bad as zero P but still not good.

So moving forward with dosing a Phosphorus additive + a carbon source

Leave the carbon dosing aside. It's a practice that is presumed to be good for a tank but in reality it's effects and limits are not well understood the results are very often mixed.

Remember that the only reason you started carbon dosing was to eliminate a nitrate problem that you never had....it was a PO4 problem the whole time. (Available NO3 is perfectly natural and unlikely to be a problem going forward.....don't preempt a non-existent problem....don't fix what isn't broke!)

 

[Martin Kuhn]

Hello Martin,

I am running three Neptune WAV pumps, and a Tunze Wavebox. I took a video of my tank, and I will *try* to post it here: If that doesn't work, I think that the flow in the tank is pretty good, as I don't really have any dead spots in the tank, and the flow is pretty random. I have two WAV pumps on the left side wall, facing one WAV pump, and the Wavebox on the opposite side.

Let me know what you suggest regarding bacteria additions?

As from the video the flow seems to be very good. I would eliminate this as "possible factor"
i can understand that you are not satisfied at all running a tank of this size and this technical equipment used, with the result you have.

- you asked for bacteria cultures that might help you. I know of several tanks with good experience using "Microbe-Lift Special blend" (Instructions for dosage come with the product).
This should "boost" bacteria of the right type for your tank and sholdn't be of any risk
- Is the lighting of your tank really as "dark" as it seems in the video. SPS need a lot of light of the proper spectrum.

 

[Lasse]

I´ll try to explain my thoughts. Sometimes it’s difficult because they are not always in the mainstream and I have to do it in a language that’s I´m not born into and do not use on a daily basis.

I will try to answer your questions in a later post because I´m short of time at the moment but just for now a remark to mcaroll´s post.

But first – some remarks

Randy state

That said, how confident are you in the nitrate kit result? Does it read zero on new salt water?

This is important because to measure NO3 in saltwater is a mess and rather difficult. There is few tests that you maybe can rely on and it could be a good idea to test with another brand. If you use the pro version of NO3 test from the same vendor as for your carbon source – that’s the brand I use and have rather good experiences of. But also that test can drive me nut sometimes. There is however one circumstance that indicate that your NO3 measurements in one or another way are right and it is the fast uptake of added phosphorous.

@mcarroll Yes – I think you are right that there is some risks in dosing a fast organic carbon source (or dosing a simple DOC – that is the scientifically term for it), However - IMO - most saltwater aquaria is to clean in order to produce this compounds for special needs (as in heterotroph denitrification and DNRA) by itself - and sometimes need a helping hand.

But it is important to handle this with soft hands and dose very carefully. The NoPOX is very potent – when I have used it – I normally start with the 25 % of the recommended dose. And all of this take time – especially in the cases there you have to do the balance trick at the edge of a sharp knife. Normally I´m using the original ethanol (Vodka) trick – but even here in very low doses – 1 ml/100 l or lower if I do not have any experiences of how just this aquaria will respond

Sincerely Lasse

 

[mcarroll]

But it is important to handle this with soft hands and dose very carefully.

+1

I think it's the goal that's very often the problem, more-so than the tool itself: Folks want to use the tool to drive P and N to zero.

Often in these cases, N-limitation will kick in and prevent real problems by stalling out the total consumption of P.

The problem really comes into effect when they finally "succeed" (often by adding GFO) and P drops to zero as well.

The organisms that thrive under these ULNS conditions are some of the nastiest toxin-generating "pest algae" there are.

 

[rocknut]

As from the video the flow seems to be very good. I would eliminate this as "possible factor"
i can understand that you are not satisfied at all running a tank of this size and this technical equipment used, with the result you have.

- you asked for bacteria cultures that might help you. I know of several tanks with good experience using "Microbe-Lift Special blend" (Instructions for dosage come with the product).
This should "boost" bacteria of the right type for your tank and sholdn't be of any risk
- Is the lighting of your tank really as "dark" as it seems in the video. SPS need a lot of light of the proper spectrum.

Thanks for the suggestion, I actually used some Microbe-Lift Special Blend in my tanks prior iteration. I'll definitely look into using that again.
Also, I think the tank just looks dark because of the exposure on my cell phone video. It is actually lit with an ATI Sunpower T5 fixture (8 x 54 watt).
Thanks again.

 

[rocknut]

Some folks hit on it already, just piling on......phosphates being unavailable is holding things back in your tank.



Watch that you don't drive N levels to zero in the process. Zero nitrates are not as bad as zero P but still not good.


Leave the carbon dosing aside. It's a practice that is presumed to be good for a tank but in reality it's effects and limits are not well understood the results are very often mixed.

Remember that the only reason you started carbon dosing was to eliminate a nitrate problem that you never had....it was a PO4 problem the whole time. (Available NO3 is perfectly natural and unlikely to be a problem going forward.....don't preempt a non-existent problem....don't fix what isn't broke!)

@mcarroll
Honestly, it was my plan to not use any carbon dosing on this tank after I re-booted 18 months ago, so long term, I would still prefer to shift over to macro algae instead. I'm not sure that I have the space in my sump to tumble a ball of chaeto, but think that an algae reactor might be doable, sitting just outside my sump. That being said, if I do in fact need to use a small dose of carbon, as some have suggested, at this point to get my tank back into balance, I'm okay with that, but would ultimately like to transition off of it. Again, I have managed to reduce my NO3 down to a level that I would assume is healthy for the tank (around 5-6) doing a series of 25% water changes over the past three weeks, and agree that my main issue is getting a measure of PO4 into the system, and getting some sort of natural balance back.

I am testing PO4 and NO3 on a nightly basis, and am planning to reduce the dose of NeoPhos once the tank seems to consistently show a level closer to 0.03 - 0.05. I am currently only dosing 2ml/day of NoPoX to the tank at this point, and am not sure yet what the best way forward is, regarding slowly eliminating it from the tank, but can deal with that later.

Thanks again.

 

[rocknut]

+1

I think it's the goal that's very often the problem, more-so than the tool itself: Folks want to use the tool to drive P and N to zero.

Often in these cases, N-limitation will kick in and prevent real problems by stalling out the total consumption of P.

The problem really comes into effect when they finally "succeed" (often by adding GFO) and P drops to zero as well.

The organisms that thrive under these ULNS conditions are some of the nastiest toxin-generating "pest algae" there are.

Just a side note: totally agree with this. The reason I ended up re-booting my tank is because I did get to ULNS levels using biopellets, and did end up with Dinoflagelates, which were hands down my worst experience in reef keeping. After trying every trick/treatment/method in the book for about four months, it was actually a high dose of NoPoX that finally beat them back. Tank just never seemed right after that however, and I started to rethink my approach, and came to the conclusion that maybe going back to live rock + skimmer + good lights & flow and maybe some macro might be a better approach (for me at least). I certainly don't remember as many threads about dinoflagelates from ten years ago.

 

[rocknut]

I´ll try to explain my thoughts. Sometimes it’s difficult because they are not always in the mainstream and I have to do it in a language that’s I´m not born into and do not use on a daily basis.

I will try to answer your questions in a later post because I´m short of time at the moment but just for now a remark to mcaroll´s post.

But first – some remarks

Randy state



This is important because to measure NO3 in saltwater is a mess and rather difficult. There is few tests that you maybe can rely on and it could be a good idea to test with another brand. If you use the pro version of NO3 test from the same vendor as for your carbon source – that’s the brand I use and have rather good experiences of. But also that test can drive me nut sometimes. There is however one circumstance that indicate that your NO3 measurements in one or another way are right and it is the fast uptake of added phosphorous.

@mcarroll Yes – I think you are right that there is some risks in dosing a fast organic carbon source (or dosing a simple DOC – that is the scientifically term for it), However - IMO - most saltwater aquaria is to clean in order to produce this compounds for special needs (as in heterotroph denitrification and DNRA) by itself - and sometimes need a helping hand.

But it is important to handle this with soft hands and dose very carefully. The NoPOX is very potent – when I have used it – I normally start with the 25 % of the recommended dose. And all of this take time – especially in the cases there you have to do the balance trick at the edge of a sharp knife. Normally I´m using the original ethanol (Vodka) trick – but even here in very low doses – 1 ml/100 l or lower if I do not have any experiences of how just this aquaria will respond

Sincerely Lasse

Thanks so much for all of this information. As I wrote in one of my other posts from this morning, I am currently only dosing 2ml/day TOTAL of NoPoX, and would eventually like to eliminate using it altogether. Look forward to some additional information when you have more time. Thanks again.

 

[Lasse]

Okay, so could I assume that by having a good amount of live rock, I do in fact have the proper area for denitrification to occur? So the fish/food will add organics and produce phosphates (as well as nitrates), but if I don't have enough phosphates, or a sufficient amount of carbon in the system, any real denitrification can't occur and the nitrates aren't processed out, and they build up? I'm assuming that with any fish in the system, phosphates are being produced, but maybe not enough in comparison to the nitrates, which doesn't allow the denitrification process to fully take place? Sorry if I'm being slow - I don't want to be too proud and not ask questions.

IMO the capability for Live rock to denitrify is very exaggerated among reefers. Yes it will be anaerobic areas deep into narrow canals in the rock but anaerobic conditions is only one of the demands for a good rate of denitrification. The second demand is a fast organic carbon source and the third is the presence of nitrate itself. If – I say if – there is a denitrification of some nitrate deep in the rocks – how will new nitrate be transported in to this area if there is not any water movement through the pores? And if it is such a movement – how do you know that the environment still will be anaerobic. Some has suggested that all of the pores has different animals that’s moving around and their movement will bring new nitrate into the pores – yes – but do we know any animals that are common in anaerobic conditions? I have very difficult to combine anaerobic pores in living rocks with continuous flow of DOC and nitrate – at least in my mind

The same problems will occur in order to explain denitrification as an pathway for nitrogen removal in swallow sand beds and pores in the back side of the grains. Flow of nutrients and still have an anaerobic situation?

Even in normal DSB – there is some problems to fully explain denitrification. it is easier in Jaubert systems and slow normal under gravel filter and reversed under gravel/DSB

So moving forward with dosing a Phosphorus additive + a carbon source (Red Sea NoPoX in my case) is the best way to go, it seems. Here is my next question: any theories on how my system evolved into its current state, being so deficient in Phosphates? Seems like typically reef systems have no/low nitrates, but fight to keep phosphates down. Any ideas on how mine might have gotten reversed?

No but I not sure that the normal is low phosphates and high nitrates in a system without different types of phosphates removal. Most people use GFO (or similar), cure their living rocks. Take away different organic compounds and so on. All of these things will favor a low level of phosphate. The main pathway for nitrogen into the aquarium (at least in newly started and aquaria without DSB and sediment traps) is not through organic matter – but through the gills of the fish. The surplus nitrogen from fishes is ta 80 – 90 % coming from direct secretion through the gills as ammonia ions (NH4)

However in more mature aquariums – especially aquariums with DSB and sediment traps – the secretion of ammonium ions (NH4) through bacterial breakdown of particle organic matter and from bacteria with capability to use DNRA can be higher. Normally this type of heterotroph bacteria breakdown is limited by fast organic carbons (DOC) – especially for the bacteria in the DNRA group

Also, by continuing to add a carbon source, and now adding Phosphorus as an additive, will my system eventually become more "balanced" so that I will have phosphate and nitrates in a more natural balance? That is what my original plan was, I guess: add some more fish to get more organics/phosphates into the system, knowing that this would of course also add nitrates, but by being ready to do some large water changes each week to keep the nitrates from climbing too high. I was reasoning that eventually the increased phosphates would be elevated enough to allow them to balance with the nitrates in a more natural ratio so more denitrification could occur? I understand that adding just phosphate to the water makes more sense, because you are not elevating nitrates at the same time, but do you think my original plan would have eventually gotten me to the same place? Albeit with MUCH more water changes

IMO to add a higher organic load to the system will be a longer way to achieve what you want and new problems will arise during the travel – in some way you can make a parallel with to use Big Bertha instead of a Salong rifle in order to kill a house sparrow

You write in other posts that you have run the aquaria as ULNS before and this can indicate that you have taken away all of the normal phosphorus reserves that you normally have in an aquaria. Reserves that automatically will be transferred to orthophosphate if the system will run low of this important nutrient.


What’s your actual NO3 level?

Sincerely Lasse