Good Nitrate to Phosphate ratio for a reef tank?

[MnFish1]

Hello!

Over the years this has been one of my favorite subjects. A while back I noticed my tanks doing a lot better with more NO3 than PO4.

When the NO3 matched the PO4 on the lower side the tank begin to grow hair algae in the sump, and dark brown algae on the rocks, overflow box, sand-bed and glass.

First let’s look at those low numbers. PO4 was down to 0.02-0.03ppm and NO3 was 1ppm.

As I bumped the the NO3 up to 3ppm...the algae begin to decrease. It continued to decrease even more as I slowly bumped it to 6ppm. Right now I’m holding it at 10ppm and the tank looks great.

I also increased the PO4 to 0.07ppm. This really got me thinking about the Red Field Ratio. Off the top of my head I think I heard you’re supposed to have 16 NO3 per 1 PO4.? Not sure how accurate that is, but would love to hear some thoughts on this subject as it may help us all.

Happy Reefing!

The Redfield ratio doesn't have any relationship to a reef tank. From what I understand. The reason being - that its only a measure of N and P in plankton - and how similar this ratio is 'all over the world'. The thought is not that N and P in the water create the ratio (i.e. its not the ratio of chemicals in the water that affect plankton - but rather conversely - that the plankton themselves affect the ratio in the water itself.

In any case - Its always an interesting discussion - but from what I've read its the amounts of the nutrients themselves rather than a ratio thats important - and in any case - certainly not the Redfield Ratio.

 

[Dan_P]

I’ll always avoid running low nutrients in a reef no matter if it’s the 1st year or 4th year. When I say low, I’m referring to PO4 at like 0.01 and NO3 at 1. Or maybe a little higher. For me, it just doesn’t work and I have issue after issue. Yet as soon as I bring them up...the tank thrives.

There’s good reason why some of the masters in this hobby run a reef the same way. All the parameters and names are listed below in Mike’s thread if you’d like to take a look.

https://www.reef2reef.com/ams/tank-parameters-of-some-masters.263/


With that said...are some people with large acropora dominated systems or refugiums packed full of cheato getting zero numbers for N & P? Well of course they are. Massive colonies and large cheato beds are sucking those nutrients up. Are the numbers really zero. Of course not! You know this by looking at bright green thriving Marcos or large Acropora colonies.

Thanks much for link. It’s always nice to see such jaw dropping beautiful reef displays.

One thing that should be clear from this article: the Redfield N ratio is probably irrelevant to reef keeping, especially when you include your closing comment about acropora dominated systems with undetectable PO4 and NO3.

It is too bad that Mike’s article missed one of the most critical questions we all ask about: how do we manage nitrate and phosphate levels. Mike’s article does not address whether or not his friends’ systems were actively managed to achieve the nitrate and phosphate levels reported. Could those levels actually be irrelevant to the “masters’s” success? Maybe the “masters’” were successful because of things they learned to practice and only know them implicitly, that is, couldn’t really tell you why they are successful. Consider how differently run their systems are from a flow perspective, and yet they are all successful. That’s the “art of reef” keeping. Mike refers to it at the end of the article. It is not really art but a learned science buried in their intuition. I suspect Mike’s friends “do things” that cause coral to grow well and probably don’t obsess about the nutrient level consequences. Look at the ranges of the parameter levels. They all work. Makes you wonder whether nitrate and phosphate levels are as important as everyone thinks?

Like most topics in this hobby, this one is amazing to follow and will fill many pages for years to come.

Dan

 

[Dan_P]

My thought is a ratio is a really poor way to think of nutrients. How does a ratio make any sense? If nitrate is 1,000 ppm, does that mean an optimal phosphate level for that tank is 10 ppm? Same at very low levels. If nitrate is 0.00001 ppm, should phosphate optimally be 0.000001 ppm?

I cannot see any reason to not independently target them at desirable levels (whatever you believe those to be, rather than targeting a ratio.

Succinctly put.

Can we drop all references to the Redfield ratio from all future nutrient level discussions? Do you have the power to decree this?

Also, I would like to suggest changing your suggestion to “target them at desirable levels that you determined empirically”.

 

[Brew12]

Succinctly put.

Can we drop all references to the Redfield ratio from all future nutrient level discussions? Do you have the power to decree this?

Also, I would like to suggest changing your suggestion to “target them at desirable levels that you determined empirically”.

I feel there is value in understanding the Redfield ratio. We shouldn't strive to maintain it, but it does show the importance of having NO3 and PO4 available. More than anything, it shows the value of having both Nitrogen and Phosphorus available in our systems. If you lack one or the other you will not grow beneficial organisms and are much more likely to have problems with cyano and dinoflagellates.

 

[MnFish1]

I feel there is value in understanding the Redfield ratio. We shouldn't strive to maintain it, but it does show the importance of having NO3 and PO4 available. More than anything, it shows the value of having both Nitrogen and Phosphorus available in our systems. If you lack one or the other you will not grow beneficial organisms and are much more likely to have problems with cyano and dinoflagellates.

Do you really think that? Why? I mean on what basis? I mean - I agree with you that having nutrients available makes sense - don't get me wrong - but that has nothing to do with the Redfield Ratio. or? BTW (unless I misunderstand exactly how this was measured - the Redfield is NOT the ratio of Nitrate to Phosphate - but rather the elemental NITROGEN and Phosphorous - which is completely different than what we measure in our tanks.

 

[Brew12]

Do you really think that? Why? I mean on what basis? I mean - I agree with you that having nutrients available makes sense - don't get me wrong - but that has nothing to do with the Redfield Ratio. or? BTW (unless I misunderstand exactly how this was measured - the Redfield is NOT the ratio of Nitrate to Phosphate - but rather the elemental NITROGEN and Phosphorous - which is completely different than what we measure in our tanks.

I think I know what you are asking, but I'm not 100% sure. Hopefully my answer will fit your question!

The Redfield ratio does state that phytoplankton, which is a mixture of all sorts of desirable life, is comprised of roughly 16 parts nitrogen and 1 part phosphorus. So what happens if you become phosphorus deficient? Dinoflagellates strains can have an N to P ratio of almost 50 to 1. This is one reason people who run too much GFO can have dino outbreaks. Once phosphorus becomes deficient conditions are better for dino's than phytoplankton. On the flip side, some strains of cyanobacteria have an N to P ratio of 5 to 1. When a system is nitrogen deficient for growing phyto it can open the door to cyano.

But you are correct, as I said earlier in this thread, we have no way of actually measuring the N and P in our systems so we shouldn't strive to maintain it. That doesn't remove the value of understanding it imo.

 

[MnFish1]

I think I know what you are asking, but I'm not 100% sure. Hopefully my answer will fit your question!

The Redfield ratio does state that phytoplankton, which is a mixture of all sorts of desirable life, is comprised of roughly 16 parts nitrogen and 1 part phosphorus. So what happens if you become phosphorus deficient? Dinoflagellates strains can have an N to P ratio of almost 50 to 1. This is one reason people who run too much GFO can have dino outbreaks. Once phosphorus becomes deficient conditions are better for dino's than phytoplankton. On the flip side, some strains of cyanobacteria have an N to P ratio of 5 to 1. When a system is nitrogen deficient for growing phyto it can open the door to cyano.

But you are correct, as I said earlier in this thread, we have no way of actually measuring the N and P in our systems so we shouldn't strive to maintain it. That doesn't remove the value of understanding it imo.

You answered it. The interesting thing - is that Redfield himself concluded in his second review of this - that it was not 'what was in the water' that caused the ratio - it was 'what was in the organisms that created the ratio found in the water. Suggesting that altering 'the water' will not change anything. Hope this makes sense

 

[Brew12]

You answered it. The interesting thing - is that Redfield himself concluded in his second review of this - that it was not 'what was in the water' that caused the ratio - it was 'what was in the organisms that created the ratio found in the water. Suggesting that altering 'the water' will not change anything. Hope this makes sense

Absolutely. It's less about knowing what is in the water than understanding the needs of what we are trying to grow in our systems.

Having extra of either in the water is fine. Running short of one or the other is a problem.

 

[MnFish1]

Dinoflagellates strains can have an N to P ratio of almost 50 to 1. This is one reason people who run too much GFO can have dino outbreaks. Once phosphorus becomes deficient conditions are better for dino's than phytoplankton. On the flip side, some strains of cyanobacteria have an N to P ratio of 5 to 1. When a system is nitrogen deficient for growing phyto it can open the door to cyano.

By the way - here is something for you to think about. Redfield thought there were 2 reasons to explain 'his ratio' - 1. That the N and P available in the water 'created' the N and P inside the organisms. 2. That the N and P in the organisms affected the concentrations of N and P in the water - kind of a 'chicken or egg' scenario. In the end he decided it was the second explanation that was happening. So - the question./comment - what if the fact that Dinos are 'growing' is causing the lower Phosphate in the water (i.e. they are affecting the concentrations in the water) - as compared to the 'low phosphate' causing dino outbreaks...??

 

[Dan_P]

By the way - here is something for you to think about. Redfield thought there were 2 reasons to explain 'his ratio' - 1. That the N and P available in the water 'created' the N and P inside the organisms. 2. That the N and P in the organisms affected the concentrations of N and P in the water - kind of a 'chicken or egg' scenario. In the end he decided it was the second explanation that was happening. So - the question./comment - what if the fact that Dinos are 'growing' is causing the lower Phosphate in the water (i.e. they are affecting the concentrations in the water) - as compared to the 'low phosphate' causing dino outbreaks...??

Has anyone been able to determine how many dinoflagellates are growing in their system and how quickly they are reproducing? If so your question might be answered with a back of an envelope calculation.

 

[BeejReef]

I'm all about learning from those with tons of experience. I'm wary of advise on N and P though. Maybe everyone is right this time, but everything I read and watched as recently as 6 months ago when planning my build was the exact opposite. People were verbally beating each other to death over 5ppm Nitrate.

Now, we're living in some weird reality where you're supposed to have $1,800 of nutrient export equipment running AND be dosing $12 bottles of nitrogen (produced in pharmaceutical-grade labs from captive-bred fish poo).

This is not a knock on anybody. It's simply an observation that there are limits to human understanding. Can't cure the cold, can't mathematically predict the weather yet. NASA can't create a stable, sealed enclosed environment for human beings... and they can explain what's not working. Add to that, there probably is not an "answer" to the ideal levels of many of the parameters... unless you can find a reef in the ocean somewhere where a coral from Australia, three from indonesia, and two from the gulf of mexico are absolutely thriving at a depth of two feet from the sun

 

[Brew12]

By the way - here is something for you to think about. Redfield thought there were 2 reasons to explain 'his ratio' - 1. That the N and P available in the water 'created' the N and P inside the organisms. 2. That the N and P in the organisms affected the concentrations of N and P in the water - kind of a 'chicken or egg' scenario. In the end he decided it was the second explanation that was happening. So - the question./comment - what if the fact that Dinos are 'growing' is causing the lower Phosphate in the water (i.e. they are affecting the concentrations in the water) - as compared to the 'low phosphate' causing dino outbreaks...??

In reality, you can't have one without the other. You can't have the chicken without the egg or the egg without the chicken. Available N and P has to impact what is available inside the organism, and what the organism takes out of the water impacts what remains in the water. Even though Dino's take much less phosphate from the water than an equivalent mass of cyanobacteria they do take some which will lower it. I do think this paper does a good job at showing the imbalance drives the shift to HAB's rather than the other way around but obviously, the two cannot be completely separated.
https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1984.29.6.1149

 

[griff500]

My thought is a ratio is a really poor way to think of nutrients. How does a ratio make any sense? If nitrate is 1,000 ppm, does that mean an optimal phosphate level for that tank is 10 ppm? Same at very low levels. If nitrate is 0.00001 ppm, should phosphate optimally be 0.000001 ppm?

I cannot see any reason to not independently target them at desirable levels (whatever you believe those to be, rather than targeting a ratio.

Would 'balance' work better than 'ratio'?

Nitrate at 1,000 ppm might be a bit of an issue for the animals in the tank...

I do think that keeping the nutrients balanced is important and that there is a range within which it can happen. I get the feeling that higher nitrate works with higher phosphate (but still at a level far lower than nitrate and within a general ratio) and the same applies to lower levels.

I'll be interested to find out at some point if the successful tanks with higher levels of nitrate and phosphate have higher levels of carbon and lower levels of carbon are found in successful tanks with lower levels of nitrate and phosphate, the important thing being the balance between them.

 

[marco fish]

Great read! And with all that said, and very well said at that !!!
So What we have to do as aquarists is just find our own happy hill and stay balanced on it. (For your own reef ‘s stability) Don’t go to far one way or the other, if not you reef is going to take a decline in either direction... To many people make the assumption that if (Bob’s) tank is doing good, wether he or she is dosing, feeding or doing any other thing out there, that there tank is going to do as good! We need to be better observers of our own reef, and do not ignore signs that we see (I wonder what’s going on and then ignore it) Test, look around for something wrong, check all of the smallest things that you can imagine, check them out! Do not make any drastic changes or abrupt decisions, because then it’s really hard to pin point a problem, you can even start another problem doing so! All that I can say from my experiences is that you might get caught in a whirlpool that you cannot swim out of... sometimes the reason for a tank crash as well.

Great information on this thread thank you for starting it @reefaholic !!!!

Happy Reefing from my Reef to Y’alls

 

[Reefahholic]

Great read! And with all that said, and very well said at that !!!
So What we have to do as aquarists is just find our own happy hill and stay balanced on it. (For your own reef ‘s stability) Don’t go to far one way or the other, if not you reef is going to take a decline in either direction... To many people make the assumption that if (Bob’s) tank is doing good, wether he or she is dosing, feeding or doing any other thing out there, that there tank is going to do as good! We need to be better observers of our own reef, and do not ignore signs that we see (I wonder what’s going on and then ignore it) Test, look around for something wrong, check all of the smallest things that you can imagine, check them out! Do not make any drastic changes or abrupt decisions, because then it’s really hard to pin point a problem, you can even start another problem doing so! All that I can say from my experiences is that you might get caught in a whirlpool that you cannot swim out of... sometimes the reason for a tank crash as well.

Great information on this thread thank you for starting it @reefaholic !!!!

Happy Reefing from my Reef to Y’alls

Thx @marco fish

 

[ramona]

Could some one please clarify for me a little bit an example of N : P ratio of 16 :1? NO3 of 10ppm divided by 16 means P of 0.62ppm?

 

[Brew12]

Could some one please clarify for me a little bit an example of N : P ratio of 16 :1? NO3 of 10ppm divided by 16 means P of 0.62ppm?

One cause of confusion is that people want to use this ratio as a ratio of NO3 to PO4 and that doesn't work. It is a measure of all sources of nitrogen and all sources of phosphorous. Nitrate and phosphate are just 2 inorganic forms of N and P. As hobbyists, we don't have an effective way to measure total N and P in our systems so it is impossible to control the ratio.

 

[Dan_P]

Could some one please clarify for me a little bit an example of N : P ratio of 16 :1? NO3 of 10ppm divided by 16 means P of 0.62ppm?

16:1 refers to the atom ratio. What you need is the molecular weight ratio of 16 nitrates to 1 phosphate. That is 10.4:1. So, if you have 10 ppm NO3, the PO4 level would be close to 1 ppm.

 

[Dan_P]

One cause of confusion is that people want to use this ratio as a ratio of NO3 to PO4 and that doesn't work. It is a measure of all sources of nitrogen and all sources of phosphorous. Nitrate and phosphate are just 2 inorganic forms of N and P. As hobbyists, we don't have an effective way to measure total N and P in our systems so it is impossible to control the ratio.

You could use Triton services to obtain the total phosphorous and total nitrogen of your water. I think that would cost $100 or more for one time point. Since the use of the Redfield ratio in the maintenance of a reef aquarium has never been shown to be of any use, the $100+ would not be money well spent.

 

[Randy Holmes-Farley]

Just to keep beating a dead horse, there’s no good rationale for targeting a ratio of N to P as opposed to targeting both values to a desirable level.