Are We Really Chasing Nitrogen or Is Phosphorus the Key?

[RobertK]

It is in the July/August issue of Coral Magazine. If you are a subscriber you can access it on-line. Title: Advanced Aquatics: Phosphate—a nutrient with diverse effects by Hans-Werner Balling

Are you guys seeing this article online? Looks like it is in the July/August issue. I just subscribed so I can read it but the latest issue I'm seeing online is the previous issue, May/June 2025.

 

[Dan_P]

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.

Thank you for the additional information. You have put much thought in feeding the systems.

My thought about the material going into each system is that we might be hard pressed saying it was identical for each system and that makes comparing aquarium appearance to residual phosphate and nitrate in the water difficult. The other possible (and controversial) conjecture is that the phosphate and nitrate concentration (within reason) play a minor role in determining aquarium appearance and coral health.

Just for fun, have you considered having Aquabiomics test the microbiome? By the way, did you say the ICP results were comparable for both systems (sorry, haven’t kept up with the thread).

 

[6272862829]

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.

Thank you for the additional information. You have put much thought in feeding the systems.

My thought about the material going into each system is that we might be hard pressed saying it was identical for each system and that makes comparing aquarium appearance to residual phosphate and nitrate in the water difficult. The other possible (and controversial) conjecture is that the phosphate and nitrate concentration (within reason) play a minor role in determining aquarium appearance and coral health.

Just for fun, have you considered having Aquabiomics test the microbiome? By the way, did you say the ICP results were comparable for both systems (sorry, haven’t kept up with the thread).

Here is the ICP for the high phosphate tank.

 

[6272862829]

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.

Thank you for the additional information. You have put much thought in feeding the systems.

My thought about the material going into each system is that we might be hard pressed saying it was identical for each system and that makes comparing aquarium appearance to residual phosphate and nitrate in the water difficult. The other possible (and controversial) conjecture is that the phosphate and nitrate concentration (within reason) play a minor role in determining aquarium appearance and coral health.

Just for fun, have you considered having Aquabiomics test the microbiome? By the way, did you say the ICP results were comparable for both systems (sorry, haven’t kept up with the thread).

Here is the low phosphate low nitrate tank. Both of these test were around the same time frame.

 

[Hans-Werner]

Btw @Hans-Werner i just finish reading your article about this on coral magazine. Great read.

Thank you very much for your feedback!

Is there a ratio you find for inorganic phosphate to organic phosphate you find yields better color/growth?

Ratios in reef tanks only matter at very low concentrations, especially at very low N (< ca. 0.2 ppm nitrate) concentrations. Corals can take up N compounds with high efficiency.

I recommend phosphate concentrations around 0.1 ppm. Higher concentrations usually don't do much harm up to at least 0.5 ppm. Upper limits are still being tested. I personally don't see much change even at 1.0 ppm, neither positive nor negative, compared to 0.2 or 0.3 ppm phosphate.

High nitrate and possibly phosphate concentrations may limit iron availability which usually is positive for coral coloration and keeping cyanos in check according to reefers that keep nitrate high like @Lasse .

 

[BriDroid]

Check this presentation out. This is a great one. Listen to what he has to say about corals been able to be ok with nitrogen limited environment but not so much with phosphorous limitations.

That was a great presentation! I got a lot out of that!

 

[reefluvrr]

It’s the latest issue of the coral magazine.

I can not find the latest July/August issue on my Coral Magazine online. I can see the May/June as my latest one in my digital edition.

Are you guys seeing this article online? Looks like it is in the July/August issue. I just subscribed so I can read it but the latest issue I'm seeing online is the previous issue, May/June 2025.

I was going to ask the same thing about the digital edition. I do not see the July/August edition out yet.

 

[RobertK]

I can not find the latest July/August issue on my Coral Magazine online. I can see the May/June as my latest one in my digital edition.

I was going to ask the same thing about the digital edition. I do not see the July/August edition out yet.

I actually emailed them today to ask about this. Here is their reply:

"The digital edition of July/August CORAL will be released in a week. We hold it back a little bit in respect of our print subscribers who are paying a premium for that physical copy. Even more so for the overseas readers who may not even have their print copies yet."

 

[reefluvrr]

I actually emailed them today to ask about this. Here is their reply:

"The digital edition of July/August CORAL will be released in a week. We hold it back a little bit in respect of our print subscribers who are paying a premium for that physical copy. Even more so for the overseas readers who may not even have their print copies yet."

Thank you for taking your time to find out the answer for us

 

[6272862829]

sorry had to remove the images.

 

[Nasty_Goblin]

In the vein of acceptable phosphate levels, does anyone have suggestions for stability?

What is an acceptable fluctuation?

 

[Troylee]

In the vein of acceptable phosphate levels, does anyone have suggestions for stability?

What is an acceptable fluctuation?

Bacto balance works very well keeping nitrates and phosphates in check! Then it’s easy to dose either one to the target you want. Acceptable range? .05-.2 I’d say is safe..

 

[Nasty_Goblin]

Bacto balance works very well keeping nitrates and phosphates in check! Then it’s easy to dose either one to the target you want. Acceptable range? .05-.2 I’d say is safe..

Thanks I'll check that out. I understand safe ranges. I'm asking how much is too much change in lets say a week?

My phosphates will climb to .25 over the course of a week and I only feed once per day.

 

[Troylee]

Thanks I'll check that out. I understand safe ranges. I'm asking how much is too much change in lets say a week?

My phosphates will climb to .25 over the course of a week and I only feed once per day.

Climbing is fine! It’s the sudden drop that does damage in my experience.. lc is brutal on sps and fish!

 

[jeremie]

Yes, this is my study. We proposed that coral growth alone may not always be a reliable indicator of overall health, as specimens exposed to elevated phosphate levels appeared more porous and potentially more susceptible to breakage during high-energy storm events.


However, this would likely not pose a concern in a controlled reef aquarium environment. Additionally, no noticeable differences in polyp extension were observed across the three experimental tanks.

Do you recall if there were any noticeable differences in the coloration of the corals during the experiment? I found it interesting that some other studies experimenting with phosphate enrichment alone didn’t find significant changes in symbiont density. This seems to align with what @Hans-Werner mentioned, as well as my personal experience — that high phosphate doesn’t seem to darken corals as much as high levels of inorganic nitrogen.

Some other papers:
Tissue and skeletal changes in the scleractinian coral Stylophora pistillata under phosphate enrichment
Nutritional control regulates symbiont proliferation and life history in coral-dinoflagellate symbiosis

 

[JD10]

Do you recall if there were any noticeable differences in the coloration of the corals during the experiment? I found it interesting that some other studies experimenting with phosphate enrichment alone didn’t find significant changes in symbiont density. This seems to align with what @Hans-Werner mentioned, as well as my personal experience — that high phosphate doesn’t seem to darken corals as much as high levels of inorganic nitrogen.

Some other papers:
Tissue and skeletal changes in the scleractinian coral Stylophora pistillata under phosphate enrichment
Nutritional control regulates symbiont proliferation and life history in coral-dinoflagellate symbiosis

Coral coloration was documented during my study, but unfortunately, it didn’t make it from my thesis into the final publication due to space limitations. I’d need to dig through some old files, but I should be able to track that data down.

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.

Your point about high phosphate not darkening corals as much as elevated inorganic nitrogen is really compelling. It’s definitely a topic that deserves more attention, especially given how many hobbyists are trying to dial in nutrient levels for optimal coloration.

 

[Randy Holmes-Farley Verified Community Expert]

Is there a ratio you find for inorganic phosphate to organic phosphate you find yields better color/growth?

Do you have a way to know or control that, aside from icp plus kit testing?

There is a tedious Hach kit, but few use it.

 

[Dan_P]

Here is the low phosphate low nitrate tank. Both of these test were around the same time frame.

Thank you for the ICP results. Something to think about.

 

[reefluvrr]

Do you have a way to know or control that, aside from icp plus kit testing?

There is a tedious Hach kit, but few use it.

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...

 

[Hans-Werner]

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...

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.