Are We Really Chasing Nitrogen or Is Phosphorus the Key?

[Hans-Werner]

We hypothesized that symbiont density increased under high nutrient conditions (as supported by other studies at the time), leading to elevated ATP production, which in turn could enhance calcification and growth. However, it’s worth noting that symbiont density itself was not measured in our study.

Not only the number of zooxanthellae may differ, also the pigment density in the individual zooanthella may differ. In theory number of zooxanthellae may remain the same and nonetheless corals get lighter since zooxanthellae reduce pigment density.

This may be a factor especially under nitrogen and/or iron limitation. Corals may not necessarily reduce number of zooxanthellae, but due to nutrient limitation zooxanthellae reduce pigment density to absorb less light.

 

[p1u5h13r4m24]

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.

I failed for years exactly for this reason.

 

[Randy Holmes-Farley Verified Community Expert]

That is a great question. One possible way I can think up of is carbon dosing.
Say if I knew I dose 4ml of vodka and it brings my PO4 level of 0.1 to 0.05, then I would assume I have an approximate 50% inorganic PO4 to 50% organic PO4. I suspect this may be an oversimplification though...

I don't think that's useful or accurate. A lot of N and P sequestered will not be suspended in the water.

 

[Randy Holmes-Farley Verified Community Expert]

Not only the number of zooxanthellae may differ, also the pigment density in the individual zooanthella may differ. In theory number of zooxanthellae may remain the same and nonetheless corals get lighter since zooxanthellae reduce pigment density.

This may be a factor especially under nitrogen and/or iron limitation. Corals may not necessarily reduce number of zooxanthellae, but due to nutrient limitation zooxanthellae reduce pigment density to absorb less light.

That's interesting. I did not know they did that.

 

[reefluvrr]

Yes, it is.

Organic phosphate isn't actually the point. The division that makes more sense is "reactive phosphate" (a category of chemical analysis) or oligophosphate on the one side and inorganic polyphosphates and organic phosphates on the other side.

In my attempts of separate analysis, most phosphate that wasn't reactive phosphate (the phosphate you find easily with colorimetric test kits and photometers) was inorganic polyphosphate and not organic phosphate. This makes sense since inorganic polyphosphates are storage phosphates of bacteria and microalgae. In my attempts of analysis the proportions where about 0.02 : 0.02 : 0.04 ppm in reactive phosphates, organic phosphates and inorganic polyphosphates. Inorganic polyphosphates were as much or more than the rest combined.

Ratios depend on turnover. I guess a bit similar to nitrate it is reactive phosphate that accumulates when concentrations are high and/or turnover is low. At low phosphate concentrations and high turnover rate it is more inorganic polyphosphates.

However, ICP analysis I have seen in forums etc. seem not to reflect my own findings. I wonder whether there have been articfacts or errors in my testing, although my results in several attempts seemed congruent.

Wow! Does this mean reactive phosphates are what corals most prefer to uptake?
It will take me time to digest this new information. Thank you @Hans-Werner

 

[reefluvrr]

I don't think that's useful or accurate. A lot of N and P sequestered will not be suspended in the water.

Thank you for correcting my assumption. I don't want to give other people false information

 

[Hans-Werner]

That's interesting. I did not know they did that.

I have to row back. I just checked it and in fact pigmentation of zooxanthellae varies mainly with light intensity while nitrogen supply, ammonia or nitrate, indeed alters number of zooxanthellae and not or little in pigment densitiy of zooxanthellae.

https://www.researchgate.net/profil...ylophora-pistillata-and-its-zooxanthellae.pdf
https://www.int-res.com/articles/meps2009/384/m384p107.pdf

 

[Hans-Werner]

Does this mean reactive phosphates are what corals most prefer to uptake?

Yes, in general only ortophosphate (reactive phosphate) is taken up. However, also polyphosphates and organic phosphates are "digested" externally with enzymes under phosphate limitation and the resulting orthophosphate is taken up.

The correct wording is orthophosphate, not oligophosphate, as written erroneously.

 

[Hans-Werner]

That's interesting. I did not know they did that.

... well, second reaction: it is more complicated and may depend on coral species and zooxanthella strain - but publications aren't extensive enough to draw a clear conclusion except adaptation in number of zooxanthellae and in zooxanthellae pigmentation are possible, maybe also as reactions to nitrogen concentration, at least in some species ...

https://www.jstage.jst.go.jp/article/fishsci1994/66/6/66_6_1006/_pdf
https://scholarspace.manoa.hawaii.edu/bitstreams/2968c605-833a-4205-b29e-574266e26793/download
... so both possibilities should be investigated if trials are done.

 

[Salem-Novel Aquatics]

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 would say that from what you're sharing you may be imbalanced in N and P - if you're experiencing browning out that's likely an increase in the symbiodinium density which may not be desirable for the coral host. The intention of my urea/ammonia article was to suggest this mixture as a supplement for systems with LOW nitrogen - not as a cocktail to be dosed no matter what (I likely did not communicate this well). I very much like Charles talk at High Tide - corals can and do thrive in low NO3 conditions in the wild which helps to balance zoox populations as well as the microbiome.

Additionally, the ratio of urea to ammonia you are dosing is somewhat high. You could be at risk of overdosing organic nitrogen without monitoring. The instructions I put in the article were 75% ammonia and 25% urea. I am not sure if you misunderstood or you are tinkering (if you are tinkering I am very interested in any other results you may have or microbiome data as I had the intention of slowly pushing urea higher anyways and see what happened - the cocktail in the article was always a conservative mixture)

Healthy corals have nitrogen fixing bacteria so even in low nitrogen conditions they can thrive. I agree with @Hans-Werner that if you're experiencing this you would see more benefit from upping P. It may be worth attempting to chase a molar ratio such as the Triton ratios or Charles suggestion. These numbers at least seem like better recommendations to me (compared to what I see as arbitrary values that are currently recommended) based on the fact Triton's are established from a large data set and Charles are derived from the literature.

But as always this is a black box problem and there's always more to learn. The "ideal" ratio between N:C:P are also likely different for corals collected from different locales who's holobionts have adapted to distinct nutrient values overtime.

 

[Salem-Novel Aquatics]

... well, second reaction: it is more complicated and may depend on coral species and zooxanthella strain - but publications aren't extensive enough to draw a clear conclusion except adaptation in number of zooxanthellae and in zooxanthellae pigmentation are possible, maybe also as reactions to nitrogen concentration, at least in some species ...

https://www.jstage.jst.go.jp/article/fishsci1994/66/6/66_6_1006/_pdf
https://scholarspace.manoa.hawaii.edu/bitstreams/2968c605-833a-4205-b29e-574266e26793/download
... so both possibilities should be investigated if trials are done.

Interesting reads - lots of ideas for experiments haha - thanks for sharing.

 

[TwelveL16]

after just fighting ostreopsis, reading this was a relief. Ill be keeping my phosphates on the higher side from now on.

 

[reefluvrr]

The instructions I put in the article were 75% ammonia and 25% urea. I am not sure if you misunderstood or you are tinkering (if you are tinkering I am very interested in any other results you may have or microbiome data as I had the intention of slowly pushing urea higher anyways and see what happened - the cocktail in the article was always a conservative mixture)

Hi Salem, Thank you for coming on to this post!

I am purposely increasing my urea as I have seen dosing only ammonia and nitrate in the past.

With the increase in dosing Urea, I noticed increase in browning on my coral colors. Pink and red sps started to look duller color. Note, they did not turn brown. Algae on my glass had to be cleaned quicker (every 1 to 1.5 days instead of 2 to 2.5 days)

Interestingly, even through dosing the urea and ammonia by an extra 3ppm equivalent of NO3 to the system, my Hana NO3 test kit still came out reading 0 at the end of the day. Because of the increase in darker coral colors, I stopped my dosing after two weeks.

 

[jeremie]

I would say that from what you're sharing you may be imbalanced in N and P - if you're experiencing browning out that's likely an increase in the symbiodinium density which may not be desirable for the coral host. The intention of my urea/ammonia article was to suggest this mixture as a supplement for systems with LOW nitrogen - not as a cocktail to be dosed no matter what (I likely did not communicate this well). I very much like Charles talk at High Tide - corals can and do thrive in low NO3 conditions in the wild which helps to balance zoox populations as well as the microbiome.

Additionally, the ratio of urea to ammonia you are dosing is somewhat high. You could be at risk of overdosing organic nitrogen without monitoring. The instructions I put in the article were 75% ammonia and 25% urea. I am not sure if you misunderstood or you are tinkering (if you are tinkering I am very interested in any other results you may have or microbiome data as I had the intention of slowly pushing urea higher anyways and see what happened - the cocktail in the article was always a conservative mixture)

Healthy corals have nitrogen fixing bacteria so even in low nitrogen conditions they can thrive. I agree with @Hans-Werner that if you're experiencing this you would see more benefit from upping P. It may be worth attempting to chase a molar ratio such as the Triton ratios or Charles suggestion. These numbers at least seem like better recommendations to me (compared to what I see as arbitrary values that are currently recommended) based on the fact Triton's are established from a large data set and Charles are derived from the literature.

But as always this is a black box problem and there's always more to learn. The "ideal" ratio between N:C:P are also likely different for corals collected from different locales who's holobionts have adapted to distinct nutrient values overtime.

I don't think the ratios matter that much if the concentrations are above the point where the uptake rates max out.

https://journals.biologists.com/jeb...383/High-phosphate-uptake-requirements-of-the
For example, this study shows that the uptake rate of nitrate in Stylophora pistillata maxed out at around 5~9 μM, which is about 0.31~0.558 ppm. So the difference between 5 ppm and 50 ppm of nitrate might not be as significant as that between 0.1 ppm and 1 ppm.
As for phosphate, the uptake rate maxed out at about 2~4 μM (0.19~0.38 ppm) in this study, which is already higher than what many people's tanks have. This might explain why many tanks could still thrive under nitrate concentrations much higher than those typically used in research papers.

I'm currently also playing around with urea dosing in some of my tanks, but I didn't bother to mix it with other nitrogen sources and just converted all my ammonium bicarbonate dosing into urea with the same amount of nitrogen. I'm now three months into urea dosing, and so far haven't observed any differences compared to when I was dosing ammonia. I do have relatively high nickel in my tanks (4~5 ppb), though, which might be a limiting factor in some tanks.