Phosphate in food

[Delphinus]

How much do you think consumption of the food would impact the PO4 cycle?

[EmilyB]

I'll put a poop collector on Moo and let ya know....

[Canadian Man]

Mitch, They are constantly foraging on the rocks/walls of the tank and Chevy eat's the sand and of course other fish poops

I do feed flake every day as well as mysis.

Deb. I'm glad to hear you would never cut back on the feeding of your fish. I did, and, well they are not suffering nor is the tank as a whole.

Oh and I do do waterchanges

[MitchM]

Randy did an article a couple of years ago on phosphate, and here are a few paragraphs:

Phosphate Sources in Reef Tanks

Organic phosphorus compounds, as well as orthophosphate, are so prevalent that any natural food will contain significant concentrations of phosphorus. Flake fish food is typically about 1% phosphorus (3% phosphate equivalent) by weight. Consequently, if 5 grams of flake food is added to a 100 gallon tank, there is the potential for the inorganic orthophosphate level to be raised by 0.4 ppm in that SINGLE FEEDING. That fact can be a significant issue for reef keepers: what to do with all of that phosphorus?

If the food is completely converted into tissue mass then there will be no excess phosphate. But much of the food that any organism consumes goes to provide energy, leaving a residue of CO2, phosphate, and a variety of nitrogen-containing compounds. A fish, whether it is an adult or a growing juvenile will consequently excrete much of the phosphorus that it takes in with food as phosphate in its waste. Of course, overfeeding will result in more delivery of phosphate than will lower feeding levels.

For those interested in knowing how much phosphorus is being exported by macroalgae, this free pdf article in the journal Marine Biology has some important information. It gives the phosphorus and nitrogen content for 9 different species of macroalgae, including many that reefkeepers maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08 % by dry weight phosphorus and 5.6% nitrogen. If one were to harvest 10 grams (dry weight) of this macroalgae from a tank, it would be the equivalent of removing 24 mg of phosphate. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67 gallon tank. All of the other species tested gave similar results (plus or minus a factor of 2). Interestingly, using nitrogen data in the same paper, it would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same tank.

The entire article is here:
http://advancedaquarist.com/issues/sept2002/chem.htm

So how are you exporting YOUR phosphates?


Mitch

[danny zubot]

Mitch said:

So how are you exporting YOUR phosphates?

That is a very good question. Myself and many other reefers don't have a whole lot of macro algae for nutrient export. It would be really helpful to devise a general idea of how much macro would be needed to export a given amount of PO4. To answer Alan's question.....

get the likely effects a sheet of nori (unconsumed) would have on 100 gallons of water?

With the same sized piece or nori you'd get a 0.0026ppm increase in 100 gallons or 380 litres of RO water.
An interesting experiment would be how much PO4 a 2.8 gram (equivelent size to the nori) piece of macro algea can export in the same 24 hour period. Then multiple that by the size of tank.

[Delphinus]

Agreed Mitch, it has to go somewhere.

Despite its pitfalls macro algae harvest I think has some benefit. I think one key element is discipline: since sporulation presumably releases back a lot of what was previously absorbed, and since you cannot guarantee the prevention of sporulation, a better focus is mitigation of the damage this would cause (long winded way of saying, if you prune often, there's less of it at any moment to dump goo into the water column).

The other pitfall that is maybe not as easy to address is the issue of allelopathy. I've found, particularly with fast growing corals such as Acropora and other SPS, that the mere presence of some macroalgaes such as caulerpa, is enough to to negatively impact the growth of SPS.

In my case I've found proximity to be a key factor, so a remote macro harvest area should likely address the issue somewhat. I'm sure it's not a perfect solution and I'm guessing that although running carbon and perhaps other absorption resins may also aid in this aspect, I'm confident none of it is a true "silver bullet" solution.

It could just be however, that the positives outweigh the negatives (if properly managed). Although ... it's probably not the worst thing in the world if (at least some of) your SPS doesn't grow as fast as it could.

And of course there are other macros that may be less pervasive than caulerpa. Chaetomorpha seems promising to me, I've never heard of any real negatives with that one. The only thing I've found with Chaeto is that it seems to require quite bright light to grow effectively. Under moderate lighting conditions it is a slow grower (at least it has been in my systems, whereas in the past where I had it under HID it was a prolific grower).

Anyhow, those are my thoughts for the moment.

[MitchM]

I've added unrinsed mysis to the first post.

Mitch

[Rikko]

A new experiment might yield some interesting results:
what about soaking the sheet on nori in RO water for some period of time before adding to the display? The test already done could be your control, now maybe soak a sheet for 5 mins and another for 15 mins and then transfer them into a fresh batch of RO water and see what PO4 says. I know nori sheets are always a little flaky/dusty, so it could be that those ragged areas are dissolving quickly. The thicker sections of the nori might not release as much into the water (though admittedly it'll still end up in the poop).

I don't know if anyone's mentioned it in this post, but has anybody tried vodka for PO4 reduction? I haven't had enough of a problem to experiment with it yet, but the feedback I've seen on the RC Chem forum has been encouraging.

[Delphinus]

Originally Posted by Carpentersreef

I've added unrinsed mysis to the first post.

Mitch, would you mind to repeat the test with rinsed mysis (and please describe the method used for rinsing, how long, etc. to try to put some kind of quantifier on it)? It would be interesting to see the difference. Thanks

[danny zubot]

Rikko said:

I don't know if anyone's mentioned it in this post, but has anybody tried vodka for PO4 reduction?

I read that those tests were not done very scientifically and that the results were based on "eye balling" the various changes. I got the impression that the reefers doing the experiment were also experimenting on themselves.

What article did you read? I'd like to compare with the one I read.