P&N Ratios Balancing the Equation

[Garf]

Used to pull out nitrates and phosphates. So if algae production stops and you have excess nitrates and phosphates you need to fix what is limiting growth which could be iron or manganese. When nutrients get low enough you shorten the lighting period so that levels are maintained.

However, if your growing algae in effective quantities, they are releasing sugars which adds a carbon source, further confusing things. The bacteria’s which proliferate off these sugars may have a large impact in reducing nutrients rather than the nutrient uptake from the algae themselves.

 

[Bruce Burnett]

However, if your growing algae in effective quantities, they are releasing sugars which adds a carbon source, further confusing things. The bacteria’s which proliferate off these sugars may have a large impact in reducing nutrients rather than the nutrient uptake from the algae themselves.

Either way we know that plants and algae require nitrates and phosphates for growth. If it was just carbon source being released by the algae then it would not be as effective in reducing phosphates. If it is a combination then it is fine. If it is sugars why do you not get the same bacterial growths as dosing? I don't need to know the why as much as how to incorporate something. I am to old to be back in school.

 

[jda]

They require nitrogen, not nitrate. Huge difference.

 

[Bruce Burnett]

They require nitrogen, not nitrate. Huge difference.

Yes but they can get the nitrogen from nitrates and of course some of the stuff like cyano can grow even with very low nitrates. Nitrates is not only source for nitrogen. You guys are going to keep me schooled.

 

[jda]

Not everything can use nitrate as a source for nitrogen. There is plenty of evidence and Lasse has given plenty more that microalgae cannot use it at all - for our purposes think Zoox. Some hosts can convert nitrate for their zoox to use, but at a cost of 30-70% that nobody really knows for sure. Some hosts cannot convert nitrate at all. Those hosts need to get their nitrogen from ammonia/ammonium, bacteria caught in slime coat or if the can effciiently catch any food. I mostly keep acropora and it does not appear that they can efficiently catch foods in our tanks, but that they can/do capture bacteria in the slime coat and use ammonia. When you follow the Venn Diagram, you kinda see that nitrate is mostly useless for corals. Nitrate can use used directly by macroalgae - all kinds, at least from what I have seen.

If the best that you can hope for is that some corals can convert nitrate at a large cost of energy, then what good is it? You are better off feeding the fish more or even dosing ammonia/ammonium. I just don't see the point of having nitrate of more than a trace or other low number. I guess that if you are trying to poison dinos/diatoms/cyano, then higher residual levels of nitrate can do this.

 

[Bruce Burnett]

Not everything can use nitrate as a source for nitrogen. There is plenty of evidence and Lasse has given plenty more that microalgae cannot use it at all - for our purposes think Zoox. Some hosts can convert nitrate for their zoox to use, but at a cost of 30-70% that nobody really knows for sure. Some hosts cannot convert nitrate at all. Those hosts need to get their nitrogen from ammonia/ammonium, bacteria caught in slime coat or if the can effciiently catch any food. I mostly keep acropora and it does not appear that they can efficiently catch foods in our tanks, but that they can/do capture bacteria in the slime coat and use ammonia. When you follow the Venn Diagram, you kinda see that nitrate is mostly useless for corals. Nitrate can use used directly by macroalgae - all kinds, at least from what I have seen.

If the best that you can hope for is that some corals can convert nitrate at a large cost of energy, then what good is it? You are better off feeding the fish more or even dosing ammonia/ammonium. I just don't see the point of having nitrate of more than a trace or other low number. I guess that if you are trying to poison dinos/diatoms/cyano, then higher residual levels of nitrate can do this.

Interesting and I dose vinegar as it is simple and cheap. I have heard of dosing ammonia just not enough to try it yet. I feed my fish plenty so I have to export more. I am not one that believes in controlling nitrates and phosphates by starving fish.

 

[Hans-Werner]

I can add a little bit to ratio and stability, I think. When dosing N and P at low nutrient concentrations a ratio may be useful. Dosing phosphate and nitrate one after the other may create very unstable conditions and concentration swings.

In my experience ratios make sense in dosing. Unbalanced dosing may cause more cyanobacterial growth than necessary. Continued unbalanced dosing may lead to buildup and rise of one nutrient.

If I would dose only one nutrient it would be phosphate although this seems to cause more cyanobacterial growth than necessary also.

These are my experiences with dosing in ratios. :)

 

[Randy Holmes-Farley Verified Community Expert]

I can add a little bit to ratio and stability, I think. When dosing N and P at low nutrient concentrations a ratio may be useful. Dosing phosphate and nitrate one after the other may create very unstable conditions and concentration swings.

In my experience ratios make sense in dosing. Unbalanced dosing may cause more cyanobacterial growth than necessary. Continued unbalanced dosing may lead to buildup and rise of one nutrient.

If I would dose only one nutrient it would be phosphate although this seems to cause more cyanobacterial growth than necessary also.

These are my experiences with dosing in ratios. :)

I understand what you are saying, but IMO, that's a concentration issue, not necessarily a ratio issue.

If you are maintaining N and P at appropriate target absolute values, regardless of what ratio of dosing is needed to attaint those levels, then that is certainly as good as dosing a specific ratio, and may be better if the fixed dosing ratio still leaves N or P at inappropriate levels (say, undetectable phosphate). :)

 

[Hans-Werner]

I understand what you are saying, but IMO, that's a concentration issue, not necessarily a ratio issue.

I know what you mean but I started dosing N and P compounds in certain molar ratios 25 years ago and I noticed already then that a certain range of ratios works better and extreme ratios work not so good, especially regarding cyanbacteria.

Nutrients have always been in the low range.

When comparing "nutrient ratios" I think we must see the difference between calcium reactors with coral rubble and CO2 and nearly all other forms of calcium and alkalinity supply. Coral rubble is a source of phosphate.

My experiences are nearly exclusively with the "all other forms of calcium and alkalinity supply". :)

 

[Randy Holmes-Farley Verified Community Expert]

I know what you mean but I started dosing N and P compounds in certain molar ratios 25 years ago and I noticed already then that a certain range of ratios works better and extreme ratios work not so good, especially regarding cyanbacteria.

Nutrients have always been in the low range.

When comparing "nutrient ratios" I think we must see the difference between calcium reactors with coral rubble and CO2 and nearly all other forms of calcium and alkalinity supply. Coral rubble is a source of phosphate.

My experiences are nearly exclusively with the "all other forms of calcium and alkalinity supply". :)

In a reef tank where phosphate is undetectable and nitrate is 25 ppm, what would you dose?

IMO, there's little reason or benefit to dosing any nitrate.

 

[Hans-Werner]

In a reef tank where phosphate is undetectable and nitrate is 25 ppm, what would you dose?

Yes, it's clear. But that was never my starting point. I either had phosphate very low and nitrate something I wasn't able to find or the tanks were freshly started at all.

I think even with lots of fish, if you never use a phosphate adsorber etc., nutrients will always be in a certain range of ratios, because feedstuff usually is of biological origin and has a certain range of ratios (but ratios may vary, depending whether there are i. e. plant proteins added or whether they contain lots of fish bones from fish meal etc.).

So it is rather the question where you are at the moment, high, medium, low or limiting in nutrients, except there is something that has altered the ratios, phosphate adsorber or calcium reactor.

 

[Randy Holmes-Farley Verified Community Expert]

So it is rather the question where you are at the moment, high, medium, low or limiting in nutrients, except there is something that has altered the ratios, phosphate adsorber or calcium reactor.

I agree, but those altering things also include new dry dead rock. It is not uncommon to find undetectable phosphate and significant nitrate in such a setting. Like this one:

https://www.reef2reef.com/threads/high-nitrate-but-0-phosphate-how-to-fix-it.758628/
"I have a 4 month old tank,"

"For the past week my phosphate has been 0 (Hanna url checker) however my nitrate is normally around 10 (although today i read 25 with salifert test kit) all other parameters are fine. I have tried to increase phos by feeding reef roid every 2-3 day. Og helps for a day then my phos drops to Zero again."

 

[Hans-Werner]

Yes, I understand and agree.

But I think it is a bit like dosing calcium and alkalinity: If you have ratios that are far from "normal" ratios and out of balance, use just one of both until your ratios are in balance, than continue with a balanced molar ratio.

If you are always dosing only calcium or alkalinity you also will create swings where always one of both is rising and the other is dropping. Then you dose only the other part because it has dropped to far and the same game starts just in reverse.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, I understand and agree.

But I think it is a bit like dosing calcium and alkalinity: If you have ratios that are far from "normal" ratios and out of balance, use just one of both until your ratios are in balance, than continue with a balanced molar ratio.

If you are always dosing only calcium or alkalinity you also will create swings where always one of both is rising and the other is dropping. Then you dose only the other part because it has dropped to far and the same game starts just in reverse.

I agree with that. :)

 

[Laith]

...It is unfortunate that it is named redfield - if was named the phyto ratio, then this would never get talked about. I am going to start referring to it as Redfield/Phyto Ratio - I welcome others to do the same....

Great idea! :beaming-face-with-smiling-eyes:

 

[Laith]

However, if your growing algae in effective quantities, they are releasing sugars which adds a carbon source, further confusing things. The bacteria’s which proliferate off these sugars may have a large impact in reducing nutrients rather than the nutrient uptake from the algae themselves.

Didn't realize that the macro algea in a refugium release sugars... Interesting point.

 

[Dennis Cartier]

I know what you mean but I started dosing N and P compounds in certain molar ratios 25 years ago and I noticed already then that a certain range of ratios works better and extreme ratios work not so good, especially regarding cyanbacteria.

Nutrients have always been in the low range.

When comparing "nutrient ratios" I think we must see the difference between calcium reactors with coral rubble and CO2 and nearly all other forms of calcium and alkalinity supply. Coral rubble is a source of phosphate.

My experiences are nearly exclusively with the "all other forms of calcium and alkalinity supply". :)

I am currently pondering the amount of phosphate that I want to include in a combined ammonium/phosphate dosing solution, and was wondering if you would be willing to share the range of safe ratios, or even a ratio in the middle of the range? If you can't due to it being proprietary info for basing TM products on, then I will understand.

 

[Dan_P]

I understand what you are saying, but IMO, that's a concentration issue, not necessarily a ratio issue.

If you are maintaining N and P at appropriate target absolute values, regardless of what ratio of dosing is needed to attaint those levels, then that is certainly as good as dosing a specific ratio, and may be better if the fixed dosing ratio still leaves N or P at inappropriate levels (say, undetectable phosphate). :)

My experience with mixed algae cultures supports this view. The amount of nitrate drives algae growth (wet mass and chlorophyll A), but if there isn’t enough phosphate, growth cannot proceed as far as when there is a high concentration of phosphate. Phosphate essentially throttles growth. There is no evidence to support that there is any special control over algae growth with a particular ratio of N : P.

A very simple model of algae growth might go like this. Light intensity drives how fast growth can occur, nitrate availability determines the maximum biomass that can accumulate and phosphate availability determines how close to that maximum is achieved. Excess phosphate or nitrate can be sent to reserve pools.

 

[Jon_W79]

I am currently pondering the amount of phosphate that I want to include in a combined ammonium/phosphate dosing solution, and was wondering if you would be willing to share the range of safe ratios, or even a ratio in the middle of the range? If you can't due to it being proprietary info for basing TM products on, then I will understand.

I think you should make an ammonium solution and a phosphate solution and dose more or less of each one depending on what is needed(at least temporarily). You could mix them together again when you find the correct ratio.

 

[Dennis Cartier]

I think you should make an ammonium solution and a phosphate solution and dose more or less of each one depending on what is needed(at least temporarily). You could mix them together again when you find the correct ratio.

I thought about doing that. Right around the time that I finished up the combined solution. :rolleyes:

I did preserve the previous ammonium only solution, so if the ratio needs tweaking, I can switch back to that and mix up a different strength phosphate solution and add another head to the Masterflex drive. So I may still use that idea.