Are We Really Chasing Nitrogen or Is Phosphorus the Key?

[Tony Thompson]

How would one take account nitrogen. Most of use rely on a nitrate reading to have a piece of mind that there’s nitrogen been supplemented in the system. For example the supplement I dose is 50% urea 25% ammonia and 25% nitrate. So relying on a nitrate reading gives me the assurance on how much to dose

Hi, just to clarify, the intention of my comment was not to highlight the need for hobbyists to measure total nitrogen, I made the comment to highlight the need to be aware that there are different forms of Nitrogen available in the aquarium.

I probably agree with you on one point as I personally would like to see an easily detectable Nitrate and phosphate level in my aquarium, just for peace of mind. However I laso have no personal reasoning to suppose what the "optimal" levels or ratios of the two I should be aiming for.

I am of the opinion that the basic long standing principles of keeping any reef aquarium are still very relevant.

My own measure of a successful hobby reef aquarium is based on the personal enjoyment it gives, as simple as that.

I wish you all a peaceful Sunday, as I sit here with my dog Benji (who is sleeping), killing some time before cooking the Sunday roast. Chatting with my fellow hobbyists on the keyboard about the endless conversations around certain parameters and watching my little mushroom corals in my 60 L aquarium swaying in the current with my two clownfish whom are all oblivious to my own theories.

 

[CHSUB]

easily detectable Nitrate and phosphate level in my aquarium, just for peace of mind

Imo, relying on hobby testing for “peace of mind” is a fundamental mistake. Feeding fish and corals and observing healthy fish and corals is all the peace of mind you need. If a hobby test kit registered any reading it is likely excess.

 

[MnFish1]

Imo, relying on hobby testing for “peace of mind” is a fundamental mistake. Feeding fish and corals and observing healthy fish and corals is all the peace of mind you need. If a hobby test kit registered any reading it is likely excess.

I think you are saying something that is true - but perhaps not beneficial for many people. In other words if you look at a tank, and it looks horrible - you know 'something is wrong' - thats true. If you look at a tank and everything looks great - there is nothing to do. However, a tank looking horrible does not tell you what is wrong - and there is no way to tell without testing - and hobby grade testing is more efficient/quick/cost effective than other methods. If you're talking about testing alkalinity, Ca and Mg every 20 minutes - and that thats not beneficial - I agree with you totally.

So - hobbyist tests have been used and correlated to other more expensive/accurate test methods and have been shown to be beneficial. If something bad is happening to my tank (while I'm observing it) - without testing available it's impossible to say what the average tank owner is supposed to do. Or am I totally missing your point

 

[Reefering1]

I think you are saying something that is true - but perhaps not beneficial for many people. In other words if you look at a tank, and it looks horrible - you know 'something is wrong' - thats true. If you look at a tank and everything looks great - there is nothing to do. However, a tank looking horrible does not tell you what is wrong - and there is no way to tell without testing - and hobby grade testing is more efficient/quick/cost effective than other methods. If you're talking about testing alkalinity, Ca and Mg every 20 minutes - and that thats not beneficial - I agree with you totally.

So - hobbyist tests have been used and correlated to other more expensive/accurate test methods and have been shown to be beneficial. If something bad is happening to my tank (while I'm observing it) - without testing available it's impossible to say what the average tank owner is supposed to do. Or am I totally missing your point

Yes, but as far as N and P go.. if you're feeding several times a day(have fat healthy fish) and corals look horrible- it's likely not N and P deficiency.

 

[CHSUB]

I think you are saying something that is true - but perhaps not beneficial for many people. In other words if you look at a tank, and it looks horrible - you know 'something is wrong' - thats true. If you look at a tank and everything looks great - there is nothing to do. However, a tank looking horrible does not tell you what is wrong - and there is no way to tell without testing - and hobby grade testing is more efficient/quick/cost effective than other methods. If you're talking about testing alkalinity, Ca and Mg every 20 minutes - and that thats not beneficial - I agree with you totally.

So - hobbyist tests have been used and correlated to other more expensive/accurate test methods and have been shown to be beneficial. If something bad is happening to my tank (while I'm observing it) - without testing available it's impossible to say what the average tank owner is supposed to do. Or am I totally missing your point

I agree…hobby testing is beneficial and I do it often, but only as a confirmation to observations. I often read about a new hobbyist with an algae problem raising nutrients because a hobby test kit registers 0. This is exactly opposite of the correct action. If algae is growing nutrients are not lacking regardless of testing.

 

[BriDroid]

My little cube runs this same way. With the HR nitrate test kit I read 0ppm even though the water has a slight pink tint to it. I recently bought the LR nitrate test kit just to be able to read something. When I have ran it a few times (it’s very involved and time consuming), I’m reading anywhere from 0.2 to 0.7ppm. So there is something there.

As far as adding N to the tank, I was using ammonium bicarbonate, but my LPS were not showing the colors I knew that had. In fact, they were really dull. I’ve since moved to amino acid dosing. I’m using Amino-Organic since it says it contains amino acids and nitrogen compounds. I dose it a couple times a week. This way I know that my corals are getting nitrogen and their colors have really started to come back.

I also dose Plus-NP daily. That adds nitrogen, phosphates, and an organic carbon source to feed bacteria.

This setup seems to work for my tank. My N stays less than 1ppm (tested weekly) and my P stays under 0.1ppm (tested every other day or so).

 

[Randy Holmes-Farley Verified Community Expert]

I would just caution that for any given observation relating to the effects of nutrients, there is someone else making just about the opposite observation. Assuming this is not just an issue of different organisms, then it suggests that kit-detectable nutrients are only telling a part of the full story.

 

[FrugalReeferJon]

There is a Rappin’ with ReefBum episode with Kenneth Wingerter, owner of Hydrospace (PNS ProBio) and studied Biology at the U of Oregon, who talks about how coral reefs are well adapted to nitrogen starvation but not to phosphorus starvation because they evolved in this type of environment. He discusses this at the 19:45 mark.

 

[areefer01]

Hobbyist have been lead to believe nutrient numbers are scary that can lead to tanks over grown with algae. It is a marketing machine driving this. I've found the hobby is more enjoyable when not worrying about it.

 

[Dan_P]

Are We Really Chasing Nitrogen or Is Phosphorus the Key?

In the reefing world, the conversation around nutrient management often centers on nitrate and phosphate levels. But after observing two very different systems over time, I’m beginning to question the traditional focus, are we really chasing the right form of nitrogen, or should we be paying more attention to phosphorus?

Let’s take a look at two reef tanks that have offered some interesting insight:

Tank 1: The Nutrient Paradox

This is an Innovative Marine 25 Lagoon system, holding about 20 gallons of total water volume. It’s a mixed reef with SPS, LPS, and soft corals. Despite being a classic example of a nitrate-deficientsystem where nitrate consistently registers zero, this tank is phosphate-rich, often maxing out the Hanna Checker, though levels occasionally dip to around 0.20 ppm.

Here’s the surprising part: the colors and coral growth in this tank have always been phenomenal. No nitrogen dosing, no nitrate traceability yet the results speak for themselves.

Tank 2: The Nitrogen-Targeted Approach

Now compare that to a 100-gallon SPS/LPS system. This tank has low nutrient levels across the board, with nitrate hovering around zero and phosphate typically between 0.03 and 0.06 ppm. To compensate, it receives a blend of urea, ammonia, and nitrate to elevate nitrate levels to about 3–5 ppm.

But even with this careful nutrient supplementation, the tank’s color and growth remain just okay. There’s no significant improvement despite targeted nitrate increases.

So What Gives?

If nitrogen alone were the missing piece, Tank 2 should be thriving. Instead, it’s the nutrient-skewed, phosphate-heavy Tank 1 that’s outperforming. This leads to a serious question:

Is it nitrogen we need to chase, or is phosphorus playing a more critical role than we’ve been led to believe?

While every reef system is different, these observations suggest it’s time to rethink the standard nutrient dogma. Perhaps the interplay between nitrogen sources and how corals and beneficial bacteria process them matters more than the numbers alone. Or maybe, in some systems, elevated phosphate isn’t the villain it’s made out to be.

One thing’s clear: the conversation around nitrate, urea, ammonia, and phosphate isn’t as black and white as it seems. Sometimes, the tank tells a different story.

Please comment with your view on this.

Not sure there is a paradox here because the two systems are not identical and we cannot compare observations. Also, comparing only two parameters that have a weak correlation to coral growth is likely to have low explanatory power. I would rather review a much bigger list of parameters for each aquarium to develop different questions.

One of many parameters I would like to see is the daily rate of nitrogen and phosphorous input into each aquarium-just thinking out loud. I don’t expect you to waste your time on this idea.

 

[CHSUB]

Hobbyist have been lead to believe nutrient numbers are scary that can lead to tanks over grown with algae. It is a marketing machine driving this. I've found the hobby is more enjoyable when not worrying about it.

From reading this forum, I would bet sales are higher on phosphate additives than phosphate reducing media.

 

[6272862829]

Not sure there is a paradox here because the two systems are not identical and we cannot compare observations. Also, comparing only two parameters that have a weak correlation to coral growth is likely to have low explanatory power. I would rather review a much bigger list of parameters for each aquarium to develop different questions.

One of many parameters I would like to see is the daily rate of nitrogen and phosphorous input into each aquarium-just thinking out loud. I don’t expect you to waste your time on this idea.

25-Gallon Lagoon Reef Tank (Mixed Reef)
This tank is home to 5 fish

Pellet Feeding: Once daily, the tank is fed a mix of 7 different AquaForest pellet foods.

Liquid Feeding: I combine all five AquaForest liquid coral foods into one container, to which I also add:
2 mL of Coral Essentials CVE+
1 drop of Coral Essentials Aminos
1 drop of AquaForest Vitality
From this mixture, I dose ¼ teaspoon once daily in addition to the pellets.

Nutrient Levels:
Currently, I have not submitted an NDOC test for nitrogen levels in this system, but I plan to soon to better understand its nutrient profile. Phosphorus is generally high, frequently maxing out on the Hanna checker; however, the latest reading is 92 ppb.

100-Gallon Reef Tank (SPS) mainly
This tank houses 21 fish.

Pellet Feeding: Is auto fed a custom blend of Reef Nutrition TDO pellets mixed with yeast every hour from 8 a.m. to 6 p.m.

Liquid Feeding: A nutrient-rich blend is dosed daily (1 tsp), containing:
Oyster Feast
Phyto Feast
Roti Feast
Arctic Pods
R.O.E.
Beta Brine
4 drops of Coral Essentials Aminos
8 mL of Coral Essentials CVE+
8 drops of AquaForest Vitality
Additional Dosing:
5 mL of AquaVitro Synthesis daily, which contains urea, ammonia, and nitrates.

Nutrient Levels:
According to NDOC testing, nitrogen levels in this system average around 1.82 ppm, while phosphorus remains stable around 12 ppb.

 

[MnFish1]

Yes, but as far as N and P go.. if you're feeding several times a day(have fat healthy fish) and corals look horrible- it's likely not N and P deficiency.

Sorry my post wasn't clear - I never said it was.

 

[JD10]

Fast forward 14 years from when that study was published, do you have any thoughts now that help explain this unexpected finding? Specifically, I wonder if it had more to do with the type of lighting available in 2011 compared to today (MH vs LED)? Our tanks are quite different now then they were 14 years ago in many ways, but especially lighting.

For my research, I used two 400W 10,000K metal halides along with two 160W actinic VHO bulbs. While my experience with LEDs isn’t extensive, I’ve become more familiar with them over time. My current home tank is lit by a combination of seven fixtures: a Kessil AP9X, four AI Primes, and two Orphek LED bars.

If I were to revisit the study, I’d certainly incorporate several upgrades, particularly in terms of monitoring equipment and powerheads. As for lighting, I’m not sure I’d move away from metal halides entirely, but I could see LEDs being used effectively as supplemental lighting. Maybe I’m just a bit old-school in that regard.

 

[carbl]

Perhaps a stupid question, but corals, bacteria etc. need certain nutrients and trace elements. Why should it matter what the levels are if they are always present in the water? Whether it's 0.05 PO4 or 0.3 or 8 micrograms of strontium or 2? If it is present and does not drop to zero, the organisms should be able to draw on it if they need it.
Or am I making a mistake in my thinking?

 

[p1u5h13r4m24]

I always thought zooxanthellaebenefit from phos more than nitrate. However I think nitrate plays an important role as well. For me whenever my nitrates and phos fall out of the 100:1 ratio I start to notice algae’s taking hold

 

[Hans-Werner]

Hi @.AcroKiller.
I personally feel phosphorus is more important than nitrogen in my mixed reef tank.
Maybe @Hans-Werner can help correct anything I may say wrongly.

About 5 years ago, I dosed nitrate in hope of getting better sps colors. In my experience, it made no appreciable difference in color or growth when I had 7 to 15ppm NO3 versus 0 ppm NO3.

Then about 1.5 years ago, I started to dose Ammonium bicarbonate. Initially I would have 0 ppm NO3 and slowly dosed Ammonium Bicarbonate daily until I can see my NO3 go up to about 3ppm.
I think by dosing this way, when I saw my NO3 reach up to a measurable number, it would mean my mixed reef system can not take up additional ammonium/ Nitrogen and now NO3 is the resultant biproduct. Again, I did not see better colors. I did have to clean my glass more frequently when my Nitrogen levels go up though. I honestly cannot say anything about improved growth from dosing ammonium as I never had fast growing corals to begin with. I felt I had good colors even without dosing ammonium, I therefore stopped dosing it for about 1 year now.

After Salem Clemens talked about dosing urea as an organic source of nitrogen, I went down the rabbit hole again. Now I am dosing 75% urea and 25% ammonium bicarbonate. I have been dosing this for daily for 2 weeks now. So far I still have 0ppm NO3 reading on my Hanna meter. I once again have to clean my glass more frequently, but one noticeable change may not be all too positive. My sps colors appeared to be more brown...
It is still too early to say anything positive or negative with urea dosing for nitrogen, but wanted to give you my experience thus far.

As far as phosphorus goes, my phosphate level is about 0.05 currently. I do carbon dose to keep my PO4 levels under 0.1. If I do not carbon dose, my PO4 levels will go above 0.3ppm. I find carbon dosing helps convert measurable inorganic phosphate to unmeasurable organic phosphate. I think this just means I still have the same amount of phosphorus, but corals uptake organic phosphate to grow.

Anyone, please correct or share your experience regarding what I just written. Thanks

I expect that more phosphate, no N dosing and ignoring nitrate more likely would bring you closer to your goals (better colors and growth).

 

[BillyW]

I must be doing something wrong. No matter how much nitrate I dose it’s always 0 and the lowest my phosphate has ever been is 0.07 and fluctuates to highest at 0.23.
Obviously the more nitrate I dose the lower my phosphates get, but no change to anything in the tank other than just less glass cleaning.
I haven’t been home in 45 days to do anything to the tank to include dose any nitrate or ammonia, and the wife sends random picture updates, and everything still looks good. Excited to see how far the phosphates have rise, and would bet a paycheck my nitrates test 0.

 

[SpartaReef]

I never test... I never chase numbers.

It's good to see these discussions beginning to take hold. There are so many cycles going on in our tanks... nitrogen and phos. And both feed algae (which corals need and have within them) but people focus on eliminating algae and end up with struggling corals in the process.

That's where macro algae helps... it keeps the hair algaes at bay while allowing your corals to flourish as they don't totally strip your water if the essentials.

But dosing helps too

 

[rtparty]

From reading this forum, I would bet sales are higher on phosphate additives than phosphate reducing media.

Not a chance. GFO and other phosphate removal medias dwarf phosphate additive sales.

The average reefer is still convinced phosphate is a villain