Nitrogen Cycling Revisited: Sand, critters, carbon, and why you may be under-feeding

[jahmic]

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​One of the most oft-discussed - if not the single most commonly mentioned - elements in the home aquarium is nitrogen. Although far from being the only element of interest to the typical reef aquarist, nitrogen is among the first elements the burgeoning aquarist learns about, and the canonical nitrogen cycle often lies at or near the center of most aquarium husbandry techniques. This attention is well deserved, of course, for the various nitrogen compounds, nitrate (NO[SUB]3[/SUB]) especially, can have a controlling impact on the function of both natural and home reef ecosystems. Of particular interest to most reef hobbyists is the effect that nitrate concentrations can have on algae growth, with many hobbyists focusing on controlling nitrate concentration as a way to limit the growth of nuisance microalgae. On a global scale, nitrogen is often considered the limiting nutrient controlling primary productivity, and although many home aquaria may deviate from this rule, nitrate control remains one of the single most effective ways to influence primary productivity in our own systems.

 

[SynDen]

Ya was just reading that article and was about to post it. Very good write up on the whole cycle of nitrogen

 

[sethsolomon]

Makes me want to try a carbon dosing source.

 

[djkms]

This is the 2nd system I have carbon dosed in. I see it as one of 3 options.

1: have very small amount of fish so the system stays in balance (import/export) - BORING!!
2: have a medium to large bioload and starve your fish to keep the balance - detrimental to the fish (this is also the route most go unfortunately)
3: Carbon dose so fish can be well fed and the system is balanced.

I prefer vinegar as it is the easiest to control. I currently feed through my auto feeder 4 times a day (NLS pellets), 1/2 sheet of Nori and 6 cubes of Selcon soaked Mysis (broken into 2 feedings per day).

My import/export is perfectly balanced by dosing 96ml of vinegar per day. I have my NO3 at .1-.2 and PO4 at .01-.02 week in and week out. I also have a fuge full of macros to help remove nitrate and more importantly keep my phosphate down. I took my GFO offline about a month ago and my PO4 levels have been holding steady with carbon/fuge for export.

Its all about balancing your export to your import. My only word of advise for those who decide to start carbon dosing: Do not bottom out your NO3/PO4 doing so. Make sure you always have a readable measurement when dosing, whether it be vinegar, vodka, bio pellets or whatever. Bottoming out your nutrients is really bad for corals as they also need those nutrients to live. If you do bottom out make sure to add things back in (amino acids come to mind) to feed the corals. Honestly I know very little about this aspect (Zeovit method I guess?) but the info is out there. I do know when I bottomed out my nutrients my corals got really pale and I lost a couple prize colonies.

 

[sethsolomon]

djkms, do you do anything to negate the effects of the 2 ph of vinegar? Also, do you have a guide on how to start up carbon dosing?

 

[SynDen]

I've never tried carbon dosing like that, although I do run carbon in my reactor. How does carbon dosing compare to that? How much more effective is it? My concern currently with doing that would be that I cant test my nitrate or nitrite level is such small increments, as a use API test kits for those and they don't scale that low. So I would certainly need better test kits to measure smaller increments.
To date nitrogen hasn't been much of a concern in my tank, but as I gradually add more fish and increase the bio load it may become more of a concern, so would like to be proactive here and ensure that it never becomes a problem

 

[djkms]

I dose 12 times a day (every 2 hours) so the impact on PH is minimal.

Here is a good article to get you started:
http://reefkeeping.com/joomla/index...ar-dosing-methodology-for-the-marine-aquarium

I think the chart is pretty conservative. You could probably double the recommendation and be OK.

 

[djkms]

I've never tried carbon dosing like that, although I do run carbon in my reactor. How does carbon dosing compare to that? How much more effective is it? My concern currently with doing that would be that I cant test my nitrate or nitrite level is such small increments, as a use API test kits for those and they don't scale that low. So I would certainly need better test kits to measure smaller increments.
To date nitrogen hasn't been much of a concern in my tank, but as I gradually add more fish and increase the bio load it may become more of a concern, so would like to be proactive here and ensure that it never becomes a problem

Wrong carbon

Carbon source - not activated carbon.

 

[jda123]

What no study ever gets to is how much carbon that you need to add, or if you are getting enough from your feedings. You add carbon every time that you feed and most of the time, this is enough if you have appropriate micro fauna and have, and have not abused, your rock and sand and your tank has finished cycling without interrupt. Personally, I feel that if you need to add carbon to process nitrogen, then you are probably did something wrong (not wrong as in it cannot work, but wrong as in the ecosystem will not develop and you will need to intervene to make it work)... but people have to if they use silica sand that won't keep the appropriate microfauna, dry/dead rock that will take years to shed dead organics and eventually get microfauna to do their job, start their tanks with organic carbon which never allows the tank to cycle, don't keep their rocks or sand clean, don't change water to introduce the trace elements that some of the microfauna need, kill massive amounts of things or all/some of the above.. It is a different story if you need to add carbon to uptake phosphates.

There are a lot of ways to get this done, and not all work for everybody. It is important that each reefer gain the appropriate self awareness and skills to know which way that they want to go. I don't dose any organic carbon or use any GFO and my tanks can handle the load with no measurable nitrate or phosphate. I feed heavily, but responsibly (as in enough that my leopard and Halichlores wrasses get 4-5+ real inches like at the Denver Aquarium, Genicanthus get to full size and tangs outgrow my tanks), clean my aragonite sand & real live rocks and change water. This will not work for everybody. Dosing carbon will also not work for everybody. Fuges and macros won't work for everybody either (especially those who don't change water or dose iron).

I did dose carbon on my FOWLR, but I used sugar dissolved in water - way easier, cheaper and more pure than most other methods. I hate the smell of vinegar, but it would have been just as good.

I feel that these articles can be somewhat dangerous to the passer-by hobbyist who might pick up vinegar dosing as a cure-all and it will make things worse. Even though most of the articles say that they are deliberate oversimplifications or warn people not to dive in without understanding, the very people who would want to dive in for a quick fix are likely the ones who will miss the very qualifications and warnings that are offered. There is no substitute for reflection, awareness and vision, but those are hard to come by in life and even harder to get by reading articles... but the articles make it seem so easy (deliberately simple). Heed the advice from the post above - don't get into organic carbon dosing on a whim - at worst, it can case a lot of short term harm if you let it get away from you; at best, it is a lifetime of dosing that you might not need... but you might.... and knowing how to tell the difference has not ever been written about that I know of.

 

[SynDen]

Wrong carbon

Carbon source - not activated carbon.

Well ya I realize it is a totally different carbon source. So do you use both or only one? I suppose you would want both since activated carbon mainly removes ammonia and other toxins and carbon dosing mainly removes nitrate and some phos. Do you use a dosing pump for your carbon dosing or mix it into top off water?

 

[djkms]

Well ya I realize it is a totally different carbon source. So do you use both or only one? I suppose you would want both since activated carbon mainly removes ammonia and other toxins and carbon dosing mainly removes nitrate and some phos. Do you use a dosing pump for your carbon dosing or mix it into top off water?

Dosing pump.

I use activated carbon to polish my water and minimize coral warfare.

 

[jda123]

Activated carbon will also absorb tons of organics that will not make it into the N cycle... unless you leave the activated carbon in the tank for long enough that bacteria start to colonize. In some tanks, GAC can be as effective as a protein skimmer.

 

[SkyShark]

don't keep their rocks or sand clean,

Slightly off topic, but can you elaborate on what you mean by this? Do you just mean keeping detritus from settling on the rock (blast with a turkey baster, etc). I'm curious what you are doing to clean the sand bed.

 

[jahmic]

Slightly off topic, but can you elaborate on what you mean by this? Do you just mean keeping detritus from settling on the rock (blast with a turkey baster, etc). I'm curious what you are doing to clean the sand bed.

If you have sufficient flow to keep detritus from settling...then IMO you are fine. That being said, most tanks have at least one spot (or several) where detritus will tend to settle. You can address this by basting the rocks with a turkey baster, having a large enough CUC to keep the areas of rock and sand clean, and/or siphoning the top layer of your sandbed.

Allowing waste to settle and accumulate on the sandbed greatly inhibits the movement of oxygen and water through that top layer of sand. Those "dead spots" typically don't support enough bacterial colonization...they aren't true anoxic zones, nor do they have enough oxygen to support a "healthy amount" of beneficial bacteria that would typically colonize that upper 1-2" layer of your sandbed. What you usually end up with in those areas is a high amount of nutrients combined with a very inefficient nutrient sink since the bacteria colony is being inhibited...what moves in next is cyanobacteria...which, being that it is one of the simplest/oldest/most resilient forms of life, will quickly out-compete your beneficial bacteria.

Keep in mind that carbon also feeds cyano as well as your beneficial bacteria. That is part of the reason why it is so important to have a large amount of microfauna and beneficial bacteria in the system that can utilize the carbon that you are adding to the system. I've looked into carbon-dosing a lot over the past couple years...and decided against it. Unless your system is healthy, mature, and balanced...it seems like the likelihood of adding to the complexity of whatever issues you are having outweighs the benefits of carbon dosing...but, that's just my humble opinion after researching the topic. Carbon dosing is definitely not a cure-all.

As for the GAC in the reactor...not the same as carbon dosing. As water passes through the GAC in the reactor, it binds compounds in the water that would typically cause a "yellowing" of the water in your tank. It polishes the water and increases clarity. Carbon dosing via something like a biopellet reactor is different...you are adding polycarbonate material to the reactor that slowly dissolves over time...which is adding soluble carbon to the tank which is then taken up by bacteria and microfauna in order to process and eventually export nutrients.

I think one of the main points of the article...as hinted by the title...is that the tank's population of microfauna is essential to long-term tank health...and their survival is dependent upon them being fed sufficiently.

 

[jda123]

If you have spots on your rocks that you constantly have to baste, then just siphon that junk. If you don't do anything, eventually the sand bed will clog with detritus and the microfauna and O2 and N2 gasses cannot move around - it becomes dead and contributes to old tank syndrome http://www.advancedaquarist.com/2006/5/aafeature2 . I stole this from a guy on RC, but think of the sandbed as an effective toilet - it really captures and processes the junk, but it needs flushed. Starting about year two, I vacuum about 5-10% of my sand every quarter when I do water changes - all the way down and thoroughly clean. This is very disruptive to the microfauna living there, which is why you cannot do too much at once. The area that you vacuumed will repopulate again very quickly. Over years 3, 4 and 5 all of the detritus is gone from the sandbed and then in year 6 or 7, I start again.

Shallow, wide-spread vacuuming is not my thing, but people do like it.

I forgot to add that dosed organic carbon is mostly consumed by waterborne bacteria which are then exported via skimmer. I have yet to see any reliable study, or even anecdotes, that shows how any microfauna benefits from dosing organic carbon if it is consumed before it gets to them - the waterborne bacteria can compete everything that I know about. I suppose that it is possible if the bacteria could feed something that feeds phyto that feeds rotifers, or something, but none of us have than kind of bio in our tanks and probably would not want it. It does it's purpose of uptaking N and P into skimmable bacteria, but I don't think that it does much for micro fuana.

Lastly, if you want a healthy microfauna population, dip and QT all of your corals. While you can treat for most parasites and pests anymore, you can really kill lots of pods, worms and other good creatures along with the pests when you do treat.

 

[jahmic]

I forgot to add that dosed organic carbon is mostly consumed by waterborne bacteria which are then exported via skimmer.

Good point...I had mentioned that in my above post, but I think it got accidentally moved and deleted when I was editing.

That was one of the reasons I decided against the bio-pellet reactor in my system. It seemed to be a much more reliable/efficient method if you are able to plumb the reactor into the intake of an external skimmer. That wasn't an option for me...and having that waterborne bacteria floating freely in the tank didn't seem like a great idea.

 

[jahmic]

I have yet to see any reliable study, or even anecdotes, that shows how any microfauna benefits from dosing organic carbon if it is consumed before it gets to them - the waterborne bacteria can compete everything that I know about. I suppose that it is possible if the bacteria could feed something that feeds phyto that feeds rotifers, or something, but none of us have than kind of bio in our tanks and probably would not want it. It does it's purpose of uptaking N and P into skimmable bacteria, but I don't think that it does much for micro fuana.

I should've been more specific in my post. I mentioned microfauna being able to benefit from carbon dosing since (from what I've read at least), the waterborn bacteria is actually consumed by some of the microfauna in the tank. Granted...this probably takes place on such a low level of efficiency that it's not nearly as reliable as skimming out that bacteria, but it is mentioned here:

The bacteria consumers [...] may respond to an EtOH-fueled bacteria population increase by increasing their own numbers as well. The most immediate bacteria consumers, the larger microfauna in the water column, may therefore experience an increase in population. [...] Some of these larger water column microfauna will be removed via skimming*, and so the overall plan of nutrient export will be realized. However, some of the introduced carbon nutrient is likely to be retained within the sedentary filter feeding livestock, and hence it will remain within the overall tank ecosystem. Presumably, as long as these end-consumers live and grow as a result of the added carbon nutrients, they pose no immediate risk for contributing to the waste nutrient level of the aquarium.

http://www.advancedaquarist.com/2011/3/aafeature

 

[SkyShark]

If you have spots on your rocks that you constantly have to baste, then just siphon that junk. If you don't do anything, eventually the sand bed will clog with detritus and the microfauna and O2 and N2 gasses cannot move around - it becomes dead and contributes to old tank syndrome http://www.advancedaquarist.com/2006/5/aafeature2 . I stole this from a guy on RC, but think of the sandbed as an effective toilet - it really captures and processes the junk, but it needs flushed. Starting about year two, I vacuum about 5-10% of my sand every quarter when I do water changes - all the way down and thoroughly clean. This is very disruptive to the microfauna living there, which is why you cannot do too much at once. The area that you vacuumed will repopulate again very quickly. Over years 3, 4 and 5 all of the detritus is gone from the sandbed and then in year 6 or 7, I start again.

Thanks, that sounds like a good plan.

I forgot to add that dosed organic carbon is mostly consumed by waterborne bacteria which are then exported via skimmer. I have yet to see any reliable study, or even anecdotes, that shows how any microfauna benefits from dosing organic carbon if it is consumed before it gets to them - the waterborne bacteria can compete everything that I know about.

Maybe this is opening a whole other can of worms, but I constantly hear that there really isn't a measurable amount of helpful (nitrifying) bacteria in the water and for this reason it doesn't make sense to use old water to help establish a new tank. This seems in contradiction with what you are saying about carbon dosing - or is it that dosing causes the bacteria in the water to increase to a more measurable amount?

 

[jahmic]

Carbon dosing increases the free-floating bacteria population...which can then be skimmed out in order to export nutrients. The bacteria that is suspended in the water column (which increases with carbon dosing) is not the same type of beneficial bacteria that we try to cultivate within the sandbed and on the live rock.

So...it's still true that the tank water does not carry a substantial amount of beneficial bacteria.

 

[djkms]

What no study ever gets to is how much carbon that you need to add, or if you are getting enough from your feedings. You add carbon every time that you feed and most of the time, this is enough if you have appropriate micro fauna and have, and have not abused, your rock and sand and your tank has finished cycling without interrupt. Personally, I feel that if you need to add carbon to process nitrogen, then you are probably did something wrong (not wrong as in it cannot work, but wrong as in the ecosystem will not develop and you will need to intervene to make it work)... but people have to if they use silica sand that won't keep the appropriate microfauna, dry/dead rock that will take years to shed dead organics and eventually get microfauna to do their job, start their tanks with organic carbon which never allows the tank to cycle, don't keep their rocks or sand clean, don't change water to introduce the trace elements that some of the microfauna need, kill massive amounts of things or all/some of the above.. It is a different story if you need to add carbon to uptake phosphates.

There are a lot of ways to get this done, and not all work for everybody. It is important that each reefer gain the appropriate self awareness and skills to know which way that they want to go. I don't dose any organic carbon or use any GFO and my tanks can handle the load with no measurable nitrate or phosphate. I feed heavily, but responsibly (as in enough that my leopard and Halichlores wrasses get 4-5+ real inches like at the Denver Aquarium, Genicanthus get to full size and tangs outgrow my tanks), clean my aragonite sand & real live rocks and change water. This will not work for everybody. Dosing carbon will also not work for everybody. Fuges and macros won't work for everybody either (especially those who don't change water or dose iron).

I did dose carbon on my FOWLR, but I used sugar dissolved in water - way easier, cheaper and more pure than most other methods. I hate the smell of vinegar, but it would have been just as good.

I feel that these articles can be somewhat dangerous to the passer-by hobbyist who might pick up vinegar dosing as a cure-all and it will make things worse. Even though most of the articles say that they are deliberate oversimplifications or warn people not to dive in without understanding, the very people who would want to dive in for a quick fix are likely the ones who will miss the very qualifications and warnings that are offered. There is no substitute for reflection, awareness and vision, but those are hard to come by in life and even harder to get by reading articles... but the articles make it seem so easy (deliberately simple). Heed the advice from the post above - don't get into organic carbon dosing on a whim - at worst, it can case a lot of short term harm if you let it get away from you; at best, it is a lifetime of dosing that you might not need... but you might.... and knowing how to tell the difference has not ever been written about that I know of.

I dont think there is anything "wrong" with my system since I carbon dose. Its a simple fact my feeding habits produce waste faster then the system can export. That is the whole point of carbon dosing, so you can feed more without getting a nutrient buildup. You claim that carbon dosing is limiting cycling. Curious to see evidence or studies on this.

My system is very well documented. I record everything. I say this because I know exactly how much carbon source is needed to break even with a certain amount of food. My system can process 1 cube of mysis, 1 sheet of nori and 4 rotations of NLS pellets per day to break even on import/export without dosing carbon. If I stuck with only feeding that much then I would have the balance you speak of. Fact is though, I have a huge bioload (I like an active tank). They could probably survive with the mentioned feedings but I want my fish to thrive, I want my mated pairs to spawn. Not to mention well fed fish really keep their aggression down and hunting(corals) to a minimum. I feed 6 cubes a a day, sheet of nori and NLS pellets and I dose 96ml per day to break even.

Every system has a limiting or saturation point. Double your feedings then a week later double that. Guaranteed you will see an increase in NO3 and PO4 levels unless you really are underfeeding. This leads me to believe the bacteria is becoming carbon limited, why else would dosing carbon allow me to bring back down NO3/PO4? Bottom line for me, I know my break even point but chose to carbon dose to allow me to feed more not because I am trying to solve a problem.

Also, there is more bacteria in the water column with carbon dosing however, there is still plenty on surface areas in the aquarium. I can see bacteria mats on my rockwork, typically on the underside. There is also a lot of life in the water that consumes bacteria, coral included. Another benefit to carbon dosing IMO.

Great discussion btw