Redfield Ratio - significant factor in reef tanks?

[Myka]

Considering all these points, I am beginning to wonder if our use of the term ULNS in aquaria is a bit of a misnomer especially if we are feeding our corals. Perhaps ULNS in practice really only means low levels of inorganic N and P (as nitrate and phosphate) in the saltwater as measured by hobbyist test kits but the "System" could have medium to high nutrient levels from organic sources. Perhaps that is exactly what we see in the ocean where corals thrive in saltwater that measures low inorganic nutrient levels but high in organisms.

This is what I've always considered to be the definition of ULNS. I've not found that ULNS thrive without the addition of organic food sources.

And if we assume corals "prefer" uptake of N and P from foods (organic sources) over inorganic sources then the inorganic N and P levels in the aquarium could be more of a factor in controlling undesirable growth of algae and bacteria than feeding corals? Or perhaps we simply cannot simulate natural coral reef levels of organic matter in an aquarium so inorganic N and P in the water do play a big factor?

That's what I was trying to get at in post #29 above. I think we're all slowly getting to this answer.

 

[Nano sapiens]

Good discussion. The ULNS acronym is a bit misleading since it implies that 'nutrients', of any type, are 'ultra low'. 'ULINS' (Ultra Low Inorganic Nutrient System) would perhaps be a better descriptive term for the hobbyist.

 

[Randy Holmes-Farley]

5. P can be bound up in the calcium carbonate and slowly releasing as it feeds corals and algae without being measurable in the saltwater by test kits.

I'm not sure what you mean by "without being measurable with a test kit". I certainly agree that phosphate can come on and come off calcium carbonate, but when it comes off (and it must come off for a coral to get it), then it will be able to be measured with a kit.

Algae might grow directly on top of the CaCO3 rock or sand, and might, for a while, intercept some of the released phosphate, but an SPS coral sticking up into the water column cannot do that.

 

[Reef_Hobbyist]

I'm not sure what you mean by "without being measurable with a test kit". I certainly agree that phosphate can come on and come off calcium carbonate, but when it comes off (and it must come off for a coral to get it), then it will be able to be measured with a kit.

Algae might grow directly on top of the CaCO3 rock or sand, and might, for a while, intercept some of the released phosphate, but an SPS coral sticking up into the water column cannot do that.

Point taken about the sticks....

 

[ksed]

Take a look at these comments. Interesting
http://www.advancedaquarist.com/blo...plankton-key-to-coral-nutrition#disqus_thread

 

[Randy Holmes-Farley]

Take a look at these comments. Interesting
http://www.advancedaquarist.com/blo...plankton-key-to-coral-nutrition#disqus_thread

Interesting. Here's the conclusion from the original paper:

"Broadly, our results shed light on the tight relationship existing between inorganic nutrient availability and heterotrophy. Moreover, it assesses the relevance of N: P stoichiometry as a determining factor for the health of the holobiont that may be adapted to specific nutrient ratios in its surrounding environment."

Note that for reference, the "elevated" levels of nitrate and phosphate that they evaluated were 0.12 ppm nitrate and 0.048 ppm phosphate, while "normal was 0.03 ppm nitrate and 0.0095 ppm phosphate.

 

[Habib(Salifert)]

I skimmed through that paper a few days ago. I have the full version

It is a paper which requires IMO quite some attention to pick out stuff interesting for us.

If I did not skim incorrectly through it, they mention that with an increase in nitrate, phosphate becomes very important fir the host to keep up producing phospholipids for the membrane and for ATP e.g.
They also mention, something we already know, that phosphate is detrimental in a too high concentration. But the really stress that minimum quatities are needed.

The zoox - host relationship probably gets disrupted/disconnected when either one of them can't keep up with the other.

There are also some speculations in that paper but interesting toughts.

 

[Habib(Salifert)]

When I read that paper, I thought we need to pull out some older papers with nitrate uptake rate experiments with increasing nitrate concentration.

Might be useful to know below which nitrate concentration the N ratio might become very critical.


Ohhh unless I am not mistaken they also mentioned that the coral starts to excrete alkaline phosphatase when phosphate concentration is too low.

 

[ksed]

If Iron is the limiting nutrient then all else may be irrelevant.

 

[Randy Holmes-Farley]

If Iron is the limiting nutrient then all else may be irrelevant.

It isn't in my tank because I dose it.

 

[Habib(Salifert)]

If Iron is the limiting nutrient then all else may be irrelevant.

J Exp Mar Bio Ecol. 2001 May 15;259(2):249-261.
Response of a scleractinian coral, Stylophora pistillata, to iron and nitrate enrichment.
Ferrier-Pagès C1, Schoelzke V, Jaubert J, Muscatine L, Hoegh-Guldberg O.

 

[Randy Holmes-Farley]

Curious. It seems in that experiment that iron and N boosted the zoox but slowed the coral growth. Maybe the zoox were actually competing with the coral for other resources, such as bicarbonate.

 

[Habib(Salifert)]

Curious. It seems in that experiment that iron and N boosted the zoox but slowed the coral growth. Maybe the zoox were actually competing with the coral for other resources, such as bicarbonate.

In their specific case/experiments there were no significant zoox related changes (density and respiration) for nitrate enrichment so they could not explain the reduced calcification by competition for inorganic carbon in that case for their experiments.

I will paste the table here. The discussion encompases a few pages and to avoid copy right issues I will paste only a small part from it which is regarding iron.

Somehow they think it might be more complicated than it appears to be???

 

[Habib(Salifert)]

And an part of the discussion....

 

[Habib(Salifert)]

"........ I know this is highly anecdotal but if i take some water between the tumb and the index finger and rub it has a different feeling if it is aquarium water or ocean water. The ocean water feels more soapy. Dissolved organic matter? Or just holidays?

Or sunscreen on the fingers, making ocean water feel soapy?

 

[Myka]

The only way we can accurately test iron at these low levels is the Triton test, correct?

 

[Randy Holmes-Farley]

The only way we can accurately test iron at these low levels is the Triton test, correct?

Triton cannot get close to NSW levels (0.006 µg/L) but might just barely detect the spiked level in the article above (0.33 µg/L) since they claim the limit of detection is 0.3 µg/L . Triton detected none (as I expected) in my tank, despite my dosing it.

here's my blurb on Triton testing of iron from my article:

http://www.reefedition.com/my-triton-testing-results-by-randy-holmes-farley/

The natural iron level varies a lot with depth, but surface seawater may have only 0.006 µg/L. The Triton LOD = 0.3 µg/L. I dose iron, and when I dose it I boost iron to roughly 1-2 µg/L, which would be detectable. This sample was taken more than a week after the last iron dosing, and none was detected as it gets depleted in the meanwhile. I’ve not yet seen a Triton test result for a real aquarium sample that had detectable iron, but that doesn’t mean these tanks are necessarily deficient. Iron is also a case where the form is critical, and ICP cannot distinguish form. Binding to organic matter, for example, can alter the bioavailability of iron.

 

[Myka]

Oh, right. I remember reading your "blurb" now. Triton isn't as useful as originally hoped for.

 

[watchguy123]

Excellent Stoyan. Great to meet you.



Yes, it is still taboo in most circles but the up and up. In the past I just used freshwater planted aquarium fertilizers, and just recently I've been using "pure" Sodium nitrate. In my own experiences, I've found the best coloration in SPS comes from around 1-3 ppm NO3 and "greater than 0"-0.06 ppm PO4. I've seen people claim up to 10 ppm NO3 even. On the higher end of NO3 this is not even close to the Redfield Ratio. I think the Redfield Ratio is mostly just usable to us in this definition as "N many times more than P". Achieving those nutrient levels via organic matter seems to arrive at a different "good" than arriving at those nutrient levels by dosing an almost literal shot of inorganic nitrate and phosphate. It just doesn't seem to have the same affect to me, but my jury is still out. My tank will "use up" about 1 ppm NO3 and 0.06 ppm PO4 per week, which interestingly is almost exactly 16:1. I'm not entirely sure what is happening to it. If it's merely being used by anaerobic bacteria and microalgae then it probably isn't positively affecting my SPS much.

Could you elaborate on what you mean by arriving at a different good. Do you believe organic nitrates and phosphates are equal to dosing inorganic versions and if not, why.

And do you think fish poop and "coral foods" are equivalent. You can sort of "dose" fish food and visualize consumption (kind of, it is at best imprecise) but coral food seems to be a real guess as to appropriate amount. And perhaps it doesn't matter, whatever is consumed or in the water column all breaks down so as long as volume of food is consistent, one can measure nitrate and phosphate levels and achieve consistent levels

In a non carbon dosed tank filled with lots of fish and SPS, I have noticed my nitrates trending down. So low, that I have added nitrate dosing.

My interest is could I instead add more organic nitrates and phosphates via heavier fish or coral foods. And then as a result, maintain a goal of 2-4 ppm nitrates or any level considered ideal. I have assumed the phosphates with increased foods would rise above desired levels and I could deal with them via lanthanum ( and remove precipitate via dosing in a filter of 10 microns or so). So as a result, could I switch from dosing inorganic nitrate to dosing organic nitrate and aggressively removing excess phosphate. I don't know what leads to a better good yet either.

 

[Myka]

Could you elaborate on what you mean by arriving at a different good. Do you believe organic nitrates and phosphates are equal to dosing inorganic versions and if not, why.

I don't. I think you achieve better coloration if you can achieve the nutrient levels via feeding the fish/corals rather than dosing chemicals. I suspect there's more at play than just nitrate and phosphate, such as the actual digestion of food particles (food or fish poop). Maybe Randy knows if there's any truth to this or whether I'm just out to lunch. I think dosing nitrate is a decent cheat.

And do you think fish poop and "coral foods" are equivalent. You can sort of "dose" fish food and visualize consumption (kind of, it is at best imprecise) but coral food seems to be a real guess as to appropriate amount. And perhaps it doesn't matter, whatever is consumed or in the water column all breaks down so as long as volume of food is consistent, one can measure nitrate and phosphate levels and achieve consistent levels

Imo, most people who try to feed SPS via the water column end up polluting their tank instead. You either need horseshoes up your butt or you need to know what you're doing. Above all, if you're going to feed the water column you need a very, VERY aggressive nutrient export system. In other words, very good flow, and a really good skimmer. Not an entry level skimmer. That's jmho though - to me, the skimmer is the insurance. You can certainly "dose" fish food with an automatic feeder, but you're limited to pellets/flake. You can guesstimate frozen food consumption by using cubes and feed the same number each week. It's not something that really needs to be precise.

In a non carbon dosed tank filled with lots of fish and SPS, I have noticed my nitrates trending down. So low, that I have added nitrate dosing.

My interest is could I instead add more organic nitrates and phosphates via heavier fish or coral foods. And then as a result, maintain a goal of 2-4 ppm nitrates or any level considered ideal. I have assumed the phosphates with increased foods would rise above desired levels and I could deal with them via lanthanum ( and remove precipitate via dosing in a filter of 10 microns or so). So as a result, could I switch from dosing inorganic nitrate to dosing organic nitrate and aggressively removing excess phosphate. I don't know what leads to a better good yet either.

The "easy" way to achieve a given amount of nutrients is to slowly add to your fish load so that your tank naturally has nutrients. I've not had an issue with phosphate build up from feeding the fish population. I have had phosphate build up from feeding the water column and overfeeding fish. Everyone's tank is different, and you have to figure out what will work best for you and your tank.