Reef Chemistry Question of the Day #71 Thanksgiving Edition

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #71


Since today is Thanksgiving (in the US, at least), we'll pick an appropriate topic: eating.

As you sit down to your Thanksgiving dinner, your fish are watching you from the tank. You've had them all for many years, and are quite attached to them. Not only do they see you overeating, but you have them on a reduced food plan to try to deal with some green hair algae that is showing up in a few places.

Feeling guilty, you decide they should get a treat today, so you give them a little extra food. Nevertheless, they consume it all while you watch.

All quality foods contain substantial phosphate in the form of various biomolecules such as DNA, RNA, phospholipids, and proteins.

What fraction of the phosphate in the foods that they eat for Thanksgiving will most likely be released (by excretion or in fecal pellets) over the next few days?

A. Less than 10%
B. 10-30%
C. 30-60%
D. Greater than 60%

Good luck and have a nice Thanksgiving!




















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[FL_Reefer]

A? Won't there bodies use most of the elements. Or convert it to other elements?
And have a happy thanks giving too Randy!

 

[FL_Reefer]

Everybody must be too full to take a stab at it, lol

 

[Zero Nitrates]

I'm going with C.

 

[redfishbluefish]

I've got to believe that other then an increase in mass, an animial is in steady state for phosphates. In a day, I've got to believe that increase in mass is insignificant, so that the phosphates IN are close to the phosphates OUT. Accordingly, my choice is D, greater than 60%. If it is not D, I'm buying about 50 fish to control my phosphate issues.....they'd be "absorbing" more then they are taking in!


And for FL, the only animal that I know of that can convert elements was the Goose that laid the golden eggs. :bigsmile:

 

[beaslbob]

D. Most all is uneaten or pooped out. The stuff digested creates the nitrogen stuff.

 

[hart24601]

I would say D too. Although I gave my fish a turkey leg and now I seem to be having a few other problems with the tank. Worst of all they have hardly touched the turkey!

 

[whixley101]

A. Less than 10%

 

[Keithcorals]

I'm guessing C just because fish waist makes such good fertilizer

 

[Randy Holmes-Farley]

And the answer is...D. Greater than 60%

For an adult fish or other organism, nearly all of the phosphate consumed is released by excretion or in fecal pellets. There is hardly any place else for it to go.

Even rapidly growing juvenile fish release most of the phosphate consumed.

The point of this question is to try to break the mentality that if fish are eating the foods, it isn't contributing to phosphate, but uneaten food does. All of the food that is added to the tank contributes nearly equally, and completely. So in terms of phosphate "problems" it does not matter at all if all the food is eaten, just how much you add (and, of course, how much phosphate you export).

This has more:

http://www.advancedaquarist.com/2012/3/chemistry

from it:

Impact of Foods on the Aquarium Phosphate Balance

Now we come to the heart of the issue. The actual amount of phosphorus present in foods and what it means. In order to understand the effects of foods, we need to understand what happens to them when added to an aquarium. Some aquarists are under the misconception that eaten foods do not contribute to the free phosphate in the water. Many aquarists are told the mantra of feeding only as much as is eaten, and they confound this idea with the assumption that when doing so, one minimizes the phosphate release. That idea is simply untrue.

A fish or other organism that eats foods takes in substantial phosphate, as shown above. But what happens to it? If the organism is not actually expanding in size (such as an adult green chromis, or a person), the phosphate that is taken in is almost entirely excreted back into the water. The only exception to that process is the very small amount of phosphorus that goes into eggs or sperm, and since in most aquaria those items are rapidly consumed by other organisms, the phosphorus will ultimately get into the water.

Growing organisms do take up a small amount of phosphorus from the diet and retain it in their growing tissues, but the emphasis is on small. A study of a fish farm with rapidly growing rainbow trout in the ocean showed that 78-82% of the phosphorus feed to the fish was lost to the environment. A second aquaculture study using normal fish foods showed that 62% of the fed phosphate was released to the environment, with 35% being released as soluble phosphate available directly to algae, and 27% as phosphorus in fecal pellets (which if not removed, will break down in an aquarium releasing the phosphate again). Another study showed that 81.5% of commercial diet phosphate was released to the environment, but that with a "special" diet with low phosphate and low fish meal this could be reduced to 64% lost. A fourth study showed that growing fish fed slightly less phosphate than they need (to optimize theoretical uptake) take up and retain different phosphate sources differently. Using a purified protein diet, they observed retention of 72% of the phosphorus, 51% retention of phosphorus from added fish bone meal, and higher levels of uptake and retention for inorganic phosphate supplements (such as sodium phosphate).

This sort of study is of concern in aquaculture settings due to environmental contamination due to the released phosphorus and nitrogen. To my knowledge, however, it has never been done in a reef aquarium. Such phosphorus balance studies have also been performed in people for many years. In adults it is clear that nearly all phosphate taken up is excreted, mostly in the urine and some in the feces. Even in young growing children, the amount of phosphorus retained from the diet is only 5-20% of that consumed, with 80-95% excreted in the urine and feces. While such studies are fairly far removed from reef aquaria, they do supporting the idea that organisms take in a lot more phosphorus than they retain, even when growing.

Consequently, reef aquarists should expect that much of the phosphorus added to a reef aquarium in the form of foods ultimately ends up in the water as phosphate. Whether that portion getting into the water is 95% or 35% won't substantially impact the conclusions below that foods add a very large amount of phosphate.

 

[Zero Nitrates]

Randy,
In your opinion, what is the best phosphate removal method?
Kyle

 

[Randy Holmes-Farley]

Lots of methods work well.

In an aquarium, I prefer GFO as a binder.
Lanthanum can also work, but I think it needs more of a track record for in tank use. Great for treating rock.
I don't prefer aluminum oxide binders, but they certainly work. My concern is released aluminum.
Organic carbon dosing and growing macroalgae/ATS also deplete phosphate to a degree that depends on how aggressive you are with those.
Skimming also helps.

I use skimming, GFO, organic carbon dosing, and growing macroalgae.

 

[beaslbob]

dern

you mean I was right?

Are you sure of the answer?


:xd:

And FWIW I prefer removing phosphates and most other wastes with algae.

 

[Randy Holmes-Farley]

dern

you mean I was right?

Are you sure of the answer?

Well, we can try to figure some strange reason that D isn't right.

 

[Cory]

Randy, does that mean the fecal matter comes out as po4? Or does it have to be broken down by bacteria?

Also how much macroalgae based on weight would need to grow to consume that po4? Maybe another question of the day!

 

[Randy Holmes-Farley]

Well, it is all different forms of phosphate, but much of it in a fecal pellet is attached to organic molecules, so-called organophosphate.

Much of the organophosphate (but not all) would be broken down before it would be taken up by organisms. I'll do the macroalgae question as a Q of the D.