NO3 and PO4, are we measuring the wrong thing?

Reef Nutrition

nickmealey

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Several months ago I caught on to fact that I was starving my corals. SPS in particular paled out and some died, but that's not the point of this thread. I've consistently measured 0.0 for both PO4 and NO3, and I've since been feeding more and I'm beginning to see some good recovery for certain coral and overall system health.

I'm convinced that we can starve our corals, especially using media like GFO. I realize there's a plethora of folks who run ULNS with success, but I'd say if you took the median tanks that are growing health coral (especially SPS), I think we'd find many at least have detectable levels of PO4 and NO3. The fix that I've heard and experienced is pretty simple: feed more (within reason)! Some folks even dose PO4 or NO3. Of course, that means keeping algae in check and such.

Here's the kicker though, there's the ocean. I've never tested it but the only thing I hear is the amount of PO4 and NO3 is hardly detectable. If this is true, is it that coral only require a very small amount of these nutrients or is it something else? Amino acids and vitamins? My observation is that bottoming out NO3 or PO4 is more of an indicator to an overall lack of nutrients in the system than actually starving the coral of those specific compounds. What do you think?
 
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sunken3

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Several months ago I caught on to fact that I was starving my corals. SPS in particular paled out and some died, but that's not the point of this thread. I've consistently measured 0.0 for both PO4 and NO3, and I've since been feeding more and I'm beginning to see some good recovery for certain coral and overall system health.

I'm convinced that we can starve our corals, especially using media like GFO. I realize there's a plethora of folks who run ULNS with success, but I'd say if you took the median tanks that are growing health coral (especially SPS), I think we'd find many at least have detectable levels of PO4 and NO3. The fix that I've heard and experienced is pretty simple: feed more (within reason)! Some folks even dose PO4 or NO3. Of course, that means keeping algae in check and such.

Here's the kicker though, there's the ocean. I've never tested it but the only thing I hear is the amount of PO4 and NO3 is hardly detectable. If this is true, is it that coral only require a very small amount of these nutrients or is it something else? Amino acids and vitamins? My observation is that bottoming out NO3 or PO4 is more of an indicator to an overall lack of nutrients in the system than actually starving the coral of those specific compounds. What do you think?
i think there are a lot of things in the ocean that we dont/cant test for in our aquariums. Also, our aquariums are closed systems and typically the bad stuff is what builds up. Oceans have so much oxygen, plant live, etc..

there are articles that state one ocean rock (ie live straight from the ocean) can make a tank perform so much better than anything you can add or dose. (there are also reasons not to get rocks straight from the ocean..)
 

biophilia

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The zooxanthellae inside of coral tissue really only provides the animal with lipids and carbohydrates, and a very small amount of organic nitrogen (amino acids) that the zoox synthesizes from (often very low concentrations of) inorganic nitrogen present in the water column. Which is why their photosynthate is often termed "junk food".

There's enough there to support the coral's basic respiration needs, but the photosynthate can only be used for growth and reproduction if additional nitrogen is available. In the nutrient-poor waters of coral reefs, most of that nitrogen is coming from a constant supply of particulate food capture of one kind or another. So it's not a surprise that nearly the entire surface area of most corals is covered in mouths.

The nitrogen coral needs can come from a lot of sources which is why so many different tank parameters are capable of growing healthy corals. They can obtain it from dissolved organic nitrogen, dissolved inorganic nitrogen (NO3 or ammonium from fish pee), particulate organic nitrogen, foods, sediment settling on the tissue surface, etc.

Ultra low nutrient tanks might work fine to support coral health if the aquarist is supplementing some amino acids (especially aspartic acid, which is needed to form proteins in the skeletal matrix and is believed to come mostly from particulate capture by the coral), has a nice high bio-load of fish supplying a steady stream of ammonium, etc. A lot of it is just that without elevated NO3 in the water, ULN tanks end up looking a lot paler than many want aesthetically speaking.

Phosphate is a little more tricky. Corals can get it as dissolved inorganic, dissolved organic, or as particulate phosphate, but unlike nitrogen, a big majority of phosphorus uptake seems to come from the inorganic dissolved PO4 in the water which is taken up by the zooxanthellae and is actively transferred across a gradient into the coral itself. This may be why corals do really poorly if PO4 is driven too low. The saving grace is that zooxanthellae are pretty good at grabbing even miniscule concentrations of PO4 (below the detectable limits of most of our test kits) which is why corals are able to stay alive and even grow adequately in ULN tanks. That's not to say they won't grow faster with more PO4 available.
 

biophilia

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One thing about rock from the ocean is that it is often colonized with quite a bit of sponge growth -- and sponges are fantastic at taking in dissolved organic waste from the water and converting it into sponge tissue cells. Those cells are then rapidly shed back into the water as particulate matter which corals, filter feeders, and other invertebrates consume as food. They're a totally free and highly efficient filter and auto-feeder all-in-one.
 

Righteous

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I think the most important difference is that the ocean is HUGE, which also means it’s a lot more stable. So although Nitrogen and Phosphorus levels are low, they are consistently available.

Our tanks are tiny by comparison, which means all of the living organisms in it are dealing with much larger fluctuations.

Running low levels in an aquarium might mean that there are times during the day when corals or other organisms that feed the corals are struggling to get access to the forms they need or want most.

So by dosing or maintaining higher levels via feeding, we’re trying to ensure there’s more wiggle room in keeping things fed.. but we then have to make sure we don’t go too high or risk algae, cyano, etc.

Basically we’re balancing on a tightrope because we have such a small volume of water to work with.
 
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ThePurple12

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Here's the kicker though, there's the ocean. I've never tested it but the only thing I hear is the amount of PO4 and NO3 is hardly detectable. If this is true, is it that coral only require a very small amount of these nutrients or is it something else? Amino acids and vitamins? My observation is that bottoming out NO3 or PO4 is more of an indicator to an overall lack of nutrients in the system than actually starving the coral of those specific compounds. What do you think?
You're forgetting that coral polyps are literally eating machines: a mouth, stinging tentacles, and a stomach is basically it. There's plenty of zooplankton available to them on the reef, but not in aquariums. They can get by without nitrate and phosphate by eating in the wild, but when you stick them in a tank with undetectable N and P, they don't do well.
 

blasterman

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The million dollar question is why nutrient levels are so much more sparse in the ocean by orders of several decimal points and we have to keep tanks at nutrient levels that would be considered ecological disaster zones if they were that way on a wild reef. I keep my tank at 5-10 ppm nitrate and .03-.1 phosphate. If either number goes lower I have issues, especially phosphate. If you have fast growing digis or montis bottom out your phosphate and watch how quick they respond.

Our tanks aren't 'too clean'. The bacterial load in captive tanks, even in ULN is far higher than a healthy reef unless you are next to a sewer run off. If a healthy wild reef had phosphate levels I keep in my tank it would be covered and inch deep with algae sludge and Green Peace boats would be circling in protest.

My theory on this is that because out captive tank have closed loop ecology with radically different bacteria loads (and C02) than wild reefs it skews the nutrient stack in some fashion where we have to super saturate it. We are missing a third part of the equation.
 

Potatohead

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I believe dissolved organics are mostly the key, and we just don't know it because we can't really test for it. This is really the only thing that explains how tanks can thrive both with high and low nutrient levels. In fact even in my own tank especially with nitrate I find the actual level isn't nearly as important and keeping a consistent feeding regimen. If I reduce feeding to reduce nitrate (which I have pretty much abandoned trying to do now) my corals always suffer.
 

Crustaceon

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I see it as either you set your tank like a buffet and have an over abundance of resources for your corals to work with at all times, or you bring them a tiny plate of food every so often. The buffet food might not be the healthiest options available but it’s there. The plated food is five star, but if you don’t serve it regularly, your corals will just starve to death. The ocean is like a five star restaurant with really good waitstaff constantly bringing tiny plates of foo-foo food for corals.
 

ThePurple12

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The million dollar question is why nutrient levels are so much more sparse in the ocean by orders of several decimal points and we have to keep tanks at nutrient levels that would be considered ecological disaster zones if they were that way on a wild reef. I keep my tank at 5-10 ppm nitrate and .03-.1 phosphate. If either number goes lower I have issues, especially phosphate. If you have fast growing digis or montis bottom out your phosphate and watch how quick they respond.

Our tanks aren't 'too clean'. The bacterial load in captive tanks, even in ULN is far higher than a healthy reef unless you are next to a sewer run off. If a healthy wild reef had phosphate levels I keep in my tank it would be covered and inch deep with algae sludge and Green Peace boats would be circling in protest.

My theory on this is that because out captive tank have closed loop ecology with radically different bacteria loads (and C02) than wild reefs it skews the nutrient stack in some fashion where we have to super saturate it. We are missing a third part of the equation.
Food! That’s what we’re missing. Corals are designed to feast on plankton!
 
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LittleFidel

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Food! That’s what we’re missing. Corals are designed to feast on plankton!
I used to see lots of copepods and other critters in my 20g, but now see very few. I have also noticed that my Favia rarely extends its feeding tentacles anymore. I’m certain they’re connected. What do you suggest - dosing some sort of plankton?
 

ThePurple12

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I used to see lots of copepods and other critters in my 20g, but now see very few. I have also noticed that my Favia rarely extends its feeding tentacles anymore. I’m certain they’re connected. What do you suggest - dosing some sort of plankton?
For LPS, you can feed things like frozen mysis or chunks of Reef Frenzy at night. In a few days the coral will start to extend its feeding tentacles more.
 
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