How useful are nitrate and phosphate test readings?

[IntrinsicReef]

TLDR: Please post a picture of your reef and include your nitrate and phosphate measurements.

-After doing thousands of tests for nitrate and phosphate over the last 20+ years on many different systems, I am still confused. I have seen tanks with undetectable NO3 and PO4 grow hair algae before my eyes. I have seen systems with 40ppm nitrate and .3ppm phosphate without a speck of algae and growing healthy coral. I just can't seem to find the pattern. New hobbyists are told to watch and manage these numbers, but we can't seem to decide what they should be. I'm beginning to think we are having the wrong conversation.

-It seems like algae and coral are utilizing these nutrients ( ammonium? some other form of phosphorus?) before they form into the compounds we are testing for. There is also an organic pool of these nutrients that we can't test for. It just seems like what we test for is a very small part of the picture.

-After many decades of hobbyists sharing test results of the world's reef tanks, I feel we should have dialed in an ideal nutrient profile. Maybe one doesn't exist. Which goes back to my point of "Why are we telling new hobbyists to concern themselves with these numbers?" Almost every time I see a person with an algae problem, the first question is "What are your nitrate and phosphate levels?" Then they get hit with a barrage of conflicting advice on what these levels should be.

-There has been talk of a "golden ratio" of nitrogen to phosphorus. Whether it is Mike Paletta observing many successful tanks at 100 to 1, or the Redfield ratio of 16-1. These ratios are often touted as responsible for specific algae/ cyano growth, as well as coral health. I have followed the 100-1 ratio for years and had success, but I have had success with other ratios. Again, I don't see a pattern (other than having more nitrogen than phosphorus in general).

-In recent years, targeting higher nutrient levels and dosing is popular for coral coloration and health. But some people find success with low nutrients and feeding their coral. Do zooxanthellae require inorganic nitrogen/phosphorus/potassium dissolved in water like terrestrial plants or can they be sated by feeding their host? Can we have low nutrient systems where the majority of nutrients are consumed by bacteria and these bacteria feed the corals? I feel like all of these are possible scenarios and are currently practiced.

-So, please post your tank and your test results. I want to see outliers like Richard Ross and whoever is the opposite low nutrient extreme. And if you know of any literature that answers these questions, please drop a link.

 

[taricha]

Personal experience, GHA is the only nuisance algae that gives me problems. I've gone back and forth occasionally, checking whether pushing the NO3 really low or pushing the PO4 really low is more helpful.
I find that my corals do fine with NO3 pushed very low, and I can slow the GHA to make less work for me and herbivores. I can push PO4 really low (carbon dosing + GFO + ensuring some NO3 present) but my corals hate it. Tissue recession / bleaching follows. This is repeatable in my system.

here's links to a pair of articles on how PO4 depletion is more stressful on corals than NO3 depletion.

The literature explanation is that corals can handle N starvation with some P around, but N elevation with P starvation is more stressful.
Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates
"...We argue, however, that the direct negative effects on the symbiosis are not necessarily caused by the nutrient enrichment itself but by the phosphorus starvation of the algal symbionts that can be caused by skewed nitrogen (N) to phosphorus (P) ratios. We exposed corals to imbalanced N-P ratios in long-term experiments and found that the undersupply of phosphate severely disturbed the symbiosis, indicated by the loss of coral biomass, malfunctioning of algal photosynthesis and bleaching of the corals. In contrast, the corals tolerated an undersupply with nitrogen at high phosphate concentrations without negative effects on symbiont photosynthesis, suggesting a better adaptation to nitrogen limitation. ...Notably, high N-P ratios in the water were clearly identified by the accumulation of uric acid crystals."
(figure 1 for pics of euphyllia under various N/P combos.)

 

[IntrinsicReef]

Very interesting article. Especially because the experiment was done in aquariums. Does anyone know how to convert this to ppm for my hobbyist brain?
"high nitrogen/low phosphorus (HN/LP = ~ 38 μM NO3−/~0.18 μM PO4−; N: P ratio = 211:1) and low nitrogen/high phosphorus (LN/HP = ~ 0.06 μM NO3−/~3.6 μM PO4−; N: P ratio = 1: 60). "

 

[jda]

We cannot dial in a nutrient profile because the forms that most coral prefer are not testable. We can test for no3 and orthophosphate or po4 only. There are test kits that can test for more than this at a cost of many hundreds of dollars, but most hobbyists do not use these.

Algae in the tank is a product of consumers (urchins, snails, fish, etc.) rather than available building blocks - I have what most consider low no3 and po4 numbers and my tank would be over run without the consumers.

Most folks do not understand that no3 and po4 are waste products and only really used as a last resort (of sorts). Nitrogen and phosphorous are important, not nitrate and phosphate.

If you understand that no3 is not a source of nitrogen that corals cannot use directly without converting it back to ammonia and that macro algae can use no3 directly, then having more than just a small trace of no3 to make sure that you have some nitrogen in the system does not seem to do anything. Nitrogen from ammonia is more important. In the end your corals are going to want to get nitrogen from ammonia/ammonium and then nitrite before they use nitrate. Like 1 ppm of nitrate is probably telling you that you are not nitrogen limited, like your eyes and GHA have seen.

Phosphorous is a bit more difficult. There have been some solid studies posted lately that corals can get phosphorous from po4, but they prefer to get it from meta/poly phosphate first for a few reasons... one, they can hold onto poly phosphate to use until later (storage) and two, they use the other things bound the polyphosphates to bind something to themselves to eject it (like a toxic scrub). Next, corals prefer phosphates in/bound-to organics. We can only test for orthophosphate - citric acid type of tests. You can have very low orthophoshpate and not be phosphorous limited with these other forms around. In most tests, the environment is not suited to all types of phosphates and ortho is added for control - in these cases, ortho is all that matters since it is all that is available, but this is not true in a real ecosystem. A good test kit like Hach will read total P (converts all other forms to ortho first) - when I had one still if my po4 read like .01 my total was like .05 or .07. The ortho reading would freak people out as being ultra-low (it is not) but when you see the other forms, there is plenty of phosphorous.

Lastly, corals only need nitrogen and phosphorous to make/repair organic tissue. They do not use it for daily use, energy or like most people think of food. Hosts can recycle building blocks like nitrogen and phosphorous for their symbionts, but this is not 100% efficient so a trace is always needed. Having excess does not help the coral - once you have enough, you have enough. Like everything else in life, excess can cause harm if the excess gets too high... sugars, nitrogen, phosphorous, sulfur, etc. In our case, while some corals will not like even a slight excess, there are many who are tolerant of moderate excess and will still thrive.

For me, I like to keep just a trace of no3 and po4 like in the .1 no3 and 1-5 ppb po4 level. Feed the fish a lot to keep the available sources of nitrogen and phosphorus in the system. Make sure that the waste products don't climb too much.

 

[IntrinsicReef]

Personal experience, GHA is the only nuisance algae that gives me problems. I've gone back and forth occasionally, checking whether pushing the NO3 really low or pushing the PO4 really low is more helpful.
I find that my corals do fine with NO3 pushed very low, and I can slow the GHA to make less work for me and herbivores. I can push PO4 really low (carbon dosing + GFO + ensuring some NO3 present) but my corals hate it. Tissue recession / bleaching follows. This is repeatable in my system.

here's links to a pair of articles on how PO4 depletion is more stressful on corals than NO3 depletion.

Fantastic articles and highly specific to my questions. It seems like corals can grow at accelerated rates in nutrient enriched water, but become more dependent on top down herbivore control of algae competition. Also, they mentioned a higher possibility of disease in higher nutrient water? Thank you for sharing

 

[Uncle99]

TLDR: Please post a picture of your reef and include your nitrate and phosphate measurements.

-After doing thousands of tests for nitrate and phosphate over the last 20+ years on many different systems, I am still confused. I have seen tanks with undetectable NO3 and PO4 grow hair algae before my eyes. I have seen systems with 40ppm nitrate and .3ppm phosphate without a speck of algae and growing healthy coral. I just can't seem to find the pattern. New hobbyists are told to watch and manage these numbers, but we can't seem to decide what they should be. I'm beginning to think we are having the wrong conversation.

-It seems like algae and coral are utilizing these nutrients ( ammonium? some other form of phosphorus?) before they form into the compounds we are testing for. There is also an organic pool of these nutrients that we can't test for. It just seems like what we test for is a very small part of the picture.

-After many decades of hobbyists sharing test results of the world's reef tanks, I feel we should have dialed in an ideal nutrient profile. Maybe one doesn't exist. Which goes back to my point of "Why are we telling new hobbyists to concern themselves with these numbers?" Almost every time I see a person with an algae problem, the first question is "What are your nitrate and phosphate levels?" Then they get hit with a barrage of conflicting advice on what these levels should be.

-There has been talk of a "golden ratio" of nitrogen to phosphorus. Whether it is Mike Paletta observing many successful tanks at 100 to 1, or the Redfield ratio of 16-1. These ratios are often touted as responsible for specific algae/ cyano growth, as well as coral health. I have followed the 100-1 ratio for years and had success, but I have had success with other ratios. Again, I don't see a pattern (other than having more nitrogen than phosphorus in general).

-In recent years, targeting higher nutrient levels and dosing is popular for coral coloration and health. But some people find success with low nutrients and feeding their coral. Do zooxanthellae require inorganic nitrogen/phosphorus/potassium dissolved in water like terrestrial plants or can they be sated by feeding their host? Can we have low nutrient systems where the majority of nutrients are consumed by bacteria and these bacteria feed the corals? I feel like all of these are possible scenarios and are currently practiced.

-So, please post your tank and your test results. I want to see outliers like Richard Ross and whoever is the opposite low nutrient extreme. And if you know of any literature that answers these questions, please drop a link.

I had little luck in the past without “knowing” and actively maintaining water chemistry, reacting to trends in changes rather than test kit fluxes.

180g, 40 sump, 50 fuge.
Temp 78
SG 1.025
Alk 10dkh
CA 465ppm
MG 1380ppm
Nitrate 1ppm
Phosphate 0.15ppm
Iodine 0.06ppm
Bi monthly, 10% water change.

Stable 30 months.
Large fuge 12 months old.

 

[IntrinsicReef]

For me, I like to keep just a trace of no3 and po4 like in the .1 no3 and 1-5 ppb po4 level

That is very opposite of many current systems in the hobby! More typical of systems from 10+ years ago. I ran low nutrient systems for over a decade usually limiting phosphate with GFO and refugiums. Having a low rate of nuisance algae growth was the paramount goal in client tanks. I have just become conflicted with having success with higher nutrient tanks as well.

Lastly, corals only need nitrogen and phosphorous to make/repair organic tissue. They do not use it for daily use, energy or like most people think of food.

I just read the above referenced articles so it is fresh on my mind. I gleaned that dissolved nitrogen and phosphorus is important for zooxanthellae growth and reproduction. Is this what you mean by "make organic tissue."

 

[IntrinsicReef]

I had little luck in the past without “knowing” and actively maintaining water chemistry, reacting to trends in changes rather than test kit fluxes.

180g, 40 sump, 50 fuge.
Temp 78
SG 1.025
Alk 10dkh
CA 465ppm
MG 1380ppm
Nitrate 1ppm
Phosphate 0.15ppm
Iodine 0.06ppm
Bi monthly, 10% water change.

Stable 30 months.
Large fuge 12 months old.

Beautiful tank with a fairly tight N: PO4 ratio. Thank you for sharing

 

[jda]

That is very opposite of many current systems in the hobby! More typical of systems from 10+ years ago. I ran low nutrient systems for over a decade usually limiting phosphate with GFO and refugiums. Having a low rate of nuisance algae growth was the paramount goal in client tanks. I have just become conflicted with having success with higher nutrient tanks as well.

My guess is that all of the tanks have high available nutrients (available nitrogen and phosphorous) and that some have higher waste products too (no3 and po4). Just because the no3 and po4 were higher in some tanks does not mean that others have been N and P limited.

In my case, the sand bed keeps the no3 low. I do have a large chaeto refugium and also multiple skimmers that happen to keep my po4 1-5 ppb. If either of these raised a bit, I probably would not notice, but it just happens so I live with it.

I can assure you that even with my no3 and po4 lower than most that my tank can be overrun with algae if it were not for the pencil, rock and pincushion urchins and the snails. I must have lazy fish since they are not that helpful. Algae can use ammonia for nitrogen and other sources of phosphorous too.

I just read the above referenced articles so it is fresh on my mind. I gleaned that dissolved nitrogen and phosphorus is important for zooxanthellae growth and reproduction. Is this what you mean by "make organic tissue."

Probably. Nitrogen and Phosphorous are building blocks of life. They are not forms energy for food or whatever people think of when they think that more is good. You need enough N and P to build new tissue so I think that "growth and reproduction" fits this bill without knowing the intention of the author. N and P are not needed for the the same amount of stable zoox to take light, make carbon/sugars and otherwise perform their jobs as symbionts for the corals.

Biom and/or Lasse posted an article that detailed how zoox get phosphorous. It appears that the hosts prefers to gather polyphosphates and supply those. They can use ortho, but IIRC they have to make poly out of the ortho for the zoox to use. In any case, po4 is usable, but not the first choice. The zoox do get their nitrogen from ammonia that the host can gather, or some of the hosts (not all) can make it out of nitrate at an additional energy cost of 30-70% (nobody knows for sure) - in any case, struggling corals don't need to waste any energy.

The main thing to know about zoox/hosts is that the building blocks are gathered slowly over time. They only really need to accumulate new building blocks to grow - this is not 100% true since while the hosts can recycle, they are not likely 100% efficient. A large coral has literally spent a lifetime accumulating what it has. This is why expulsion events are so catastrophic - most corals can never catch up again since they are not made to gather en masse even if there is an abundance of stuff that they need floating around them.

Since you have been around, you have seen that tanks that always had heavy import have succeeded. Heavy export is a good idea too. Throughput. That is true today the same as it always was. Feed a lot and skim/fuge/whatever a lot and things work out great. Available > residual.

 

[jda]

BTW - when Dr. RHF sees this, he will likely indicate that the Redfield ratio does not apply and that any tying of the optimal range of one compound to another through a ratio is folly. Keep the appropriate ranges independently.

I agree.

 

[IntrinsicReef]

I can assure you that even with my no3 and po4 lower than most that my tank can be overrun with algae if it were not for the pencil, rock and pincushion urchins and the snails.

I fully understand that algae in not controlled by manipulating no3 and po4. That was a big part of my original post. Why do people advise newer hobbyists dealing with algae to check and change these parameters? I feel like a more appropriate response is just a list of fish and inverts that will graze the algae. That said, in established tanks with an abundance of coral, the coral seems to outcompete the algae for nutrients, and algae is less likely to grow.

 

[IntrinsicReef]

BTW - when Dr. RHF sees this, he will likely indicate that the Redfield ratio does not apply and that any tying of the optimal range of one compound to another through a ratio is folly. Keep the appropriate ranges independently.

I agree.

I look forward to that. These ratios are so commonly referenced in the hobby that I tried to find a pattern in my systems. As I originally said, I couldn't. They are even referenced in the above linked scientific articles. They are everywhere, and if they make no sense, then I would love to stop talking about them. From the linked articles above: "We exposed corals to imbalanced N: P ratios in long-term experiments and found that the undersupply of phosphate severely disturbed the symbiosis" and "Notably, high N: P ratios in the water were clearly identified by the accumulation of uric acid crystals." Just in the introduction

 

[jda]

Why do people advise newer hobbyists dealing with algae to check and change these parameters?

I wish that I knew. I often feel that this is mostly like just noobie internet parroting along the lines of...

1. once your tank can handle a bit of ammonia, then the cycle is done - as if cycles are ever done
2. dose no3 and po4 to FEED your corals
3. inch per gallon fish size rules
4. corals only need blue light
5. wet rock is the same as live rock
6. bacteria and pods from a bottle is diversity

At some point, it is likely helpful ignorance?

For me, the presence of other things on the rocks and sand keep the algae from growing as much. Live coralline, sponges, film bacteria and algae all keep the nasty algaes from growing on the surfaces. In the olden days rocks came coated with these things already... now folks are dealing with tons of vacant space for the nasty things to grow since they watched a BRS video about how their dry rock has no pests.

I guess BRS needs to make a video about how snail, hermits, urchins, etc. control algae and maybe people will listen, but they don't sell those.. so videos about scrubbers, supplements, etc.

 

[taricha]

HN/LP = ~ 38 μM NO3−/~0.18 μM PO4−

2.3ppm NO3, 0.017ppm PO4.

LN/HP = ~ 0.06 μM NO3−/~3.6 μM PO4−

.004ppm NO3, 0.34ppm PO4.

As JDA would note, these numbers represent all the N and P available in the water in their experiment.

Some hobbyists can probably get measurements like the ones in the HN/LP group that got bad outcomes, and actually have great corals - because they feed other things, so those measurements don't represent all the N and P available in the hobby water.

 

[jda]

I look forward to that. These ratios are so commonly referenced in the hobby that I tried to find a pattern in my systems. As I originally said, I couldn't. They are even referenced in the above linked scientific articles. They are everywhere, and if they make no sense, then I would love to stop talking about them. From the linked articles above: "We exposed corals to imbalanced N: P ratios in long-term experiments and found that the undersupply of phosphate severely disturbed the symbiosis" and "Notably, high N: P ratios in the water were clearly identified by the accumulation of uric acid crystals." Just in the introduction

It has been a while since I read that second article, but IIRC the issue that I had with it is that in their artificial ecosystem, they only had po4 for phosphorous since the other (more preferred?) sources were not present. I do not think that you can apply this to a reef tank or real ecosystem where other phosphorous sources are present. ...so their ratios and conclusions are only fit for them.

For example, if you are feeding your fish a lot and have an abundance of poly phosphates and a coral prefers these, then who cares what the orthophosphate ratio is at all. The same is true if you have an ecosystem with abundant types of bacteria that can be caught and assimilated in the slime coats - no need to catch any inorganic phosphate at all if you have phosphorous from the organic sources.

YMMV, of course.

 

[IntrinsicReef]

It has been a while since I read that second article, but IIRC the issue that I had with it is that in their artificial ecosystem, they only had po4 for phosphorous since the other (more preferred?) sources were not present. I do not think that you can apply this to a reef tank or real ecosystem where other phosphorous sources are present. ...so their ratios and conclusions are only fit for them.

For example, if you are feeding your fish a lot and have an abundance of poly phosphates and a coral prefers these, then who cares what the orthophosphate ratio is at all. The same is true if you have an ecosystem with abundant types of bacteria that can be caught and assimilated in the slime coats - no need to catch any inorganic phosphate at all if you have phosphorous from the organic sources.

YMMV, of course.

Yes, and the nitrogen was almost all nitrate. "The ammonium levels found in our mesocosm are very low (< 0.7% of total dissolved inorganic nitrogen) compared to the combined nitrite (~ 10%) and nitrate concentrations (~ 90%) (Wiedenmann et al., 2013). Therefore, the measured NO3− concentrations (combined NO2−/NO3−) represent largely the total dissolved inorganic nitrogen pool that could be accessed by the zooxanthellae in the present experiment."
I was curious if this was a good representation of nitrogen in our reef tanks. I'm guessing not since it was a tightly controlled lab tank.

 

[JayM]

My tank is only 3-4 months old. All of the LPS were frags added 6-7 weeks ago and most have doubled in size. GSP colony is probably triple what is was when I added it. Xenia has doubled in just a couple of weeks.

My nitrates are mid to high teens usually, but have seen them in the mid 20’s. PHOS has been .3-.4 (not a typo) for about 3 weeks now. I’m torn on whether or not to do anything about it because it doesn’t seem to be negatively affecting anything.

 

[jda]

Yes, and the nitrogen was almost all nitrate. "The ammonium levels found in our mesocosm are very low (< 0.7% of total dissolved inorganic nitrogen) compared to the combined nitrite (~ 10%) and nitrate concentrations (~ 90%) (Wiedenmann et al., 2013). Therefore, the measured NO3− concentrations (combined NO2−/NO3−) represent largely the total dissolved inorganic nitrogen pool that could be accessed by the zooxanthellae in the present experiment."
I was curious if this was a good representation of nitrogen in our reef tanks. I'm guessing not since it was a tightly controlled lab tank.

For me, I like to read stuff like that even if it does not apply to us. There is nearly always something else in there that you can learn... breadcrumbs to maybe use later on when reading another article. Unfortunately since nobody studies reef tanks, this is all that we have (along with ocean studies which often have their own issues). You HAVE TO read between the lines, think a bit and then piece together the clues and stuff.

If the only source of nitrogen that they had was no3, then the corals had to spend an awful lot of energy making ammonium, so how did that affect their health? Maybe they were OK, but they could have had even more energy to use for something else. Somebody once compared nitrate to ammonium conversion to having a day's worth of food (2000-2500 calories) a marathon away... you can make that journey to get food every once in a while but eventually your output outweighs your input.

I have read other papers where the people doing the study did not know that zoox could not use no3 directly - some addressed it after peer review or in revisions.

 

[jda]

The ammonium levels found in our mesocosm are very low (< 0.7% of total dissolved inorganic nitrogen)

...or maybe that small amount of ammonia was enough that the corals were not nitrogen limited in any way. If this is the case, then who cares about the nitrate number at all for any reason?

This is another reason why I have no use for no3 and po4 ratios.

EDIT: I guess that we can care about the nitrate numbers as a waste product or poison. I still do not care about a ratio. no3 is a poison to every living thing at high enough of a level. People often use higher no3 to poison, or growth limit, dinos. Some corals can hand many hundreds of ppm of nitrate whereas some start to suffer and will die at 10 ppm, or less. I guess with everything in life, we have to worry about enough and then too much... all at the same time.

 

[IntrinsicReef]

My tank is only 3-4 months old. All of the LPS were frags added 6-7 weeks ago and most have doubled in size. GSP colony is probably triple what is was when I added it. Xenia has doubled in just a couple of weeks.

My nitrates are mid to high teens usually, but have seen them in the mid 20’s. PHOS has been .3-.4 (not a typo) for about 3 weeks now. I’m torn on whether or not to do anything about it because it doesn’t seem to be negatively affecting anything.

Looks like a healthy young reef. Thanks for sharing