RDSB v Chaetomorph

[jriechel]

I've just spent the whole day reading through most of the threads regarding RDSB and a few on refugia. I've got more to read, true, however one issue eludes me in the material that I have already read: what's the point of a refugium with rolling Chaetomorph if you have a functioning RDSB?

I was under the impression that the Chaetomorph was for nutrient (nitrates primarily) export due to growth and removal. Reading up on RDSB, the Chaetomorph method seems very inefficient, yet I read a few posts where some of our advanced friends have both.

New hypothesis: a rolling Chaetomorph refugium's fundamental purpose is as a pH "buffer", through carbon dioxide uptake vis a vis carbonic acid reduction, when illuminated on an opposite light cycle to the display tank.

Correct, or does rolling Chaetomorph remove significant secondary nutrients such as phosphates?

 

[Cope]

Uh.....I pick B...


I think the answer is the second option, removes more than nitrates. I thought cheato was more to remove Po4 than Nitrates. I will say after adding some Cheato my tank looks way better, not to mention it's a great place to grow pods.By lighting the Cheato when your tank lights are off you can help reduce nighttime PH swings.

 

[Randy Holmes-Farley]

Growing macroalgae reduces phosphate as well as nitrate. It also exports metals. Sand beds do not. That's the huge difference and makes macroalgae a big plus over sand beds, IMO.

I actually choose to use Caulerpa racemosa, but I know that most prefer Chaetomorpha for its lack of invasiveness, despite potentially being less efficient (at least in some systems). I light mine 24/7.

 

[sjm817]

I just replaced my 30G fuge this weekend with a 65G 36Lx18Wx24T. I did both the DSB and macro. I used 300# of playsand which wound up being ~ 9" deep. This still leaves a good size area of the fuge for macro.

I've never had a DSB and wanted to try it out. Is the 9" depth good, too deep, not deep enough? How long before it becomes active?

 

[Agu]

I export nutrients via harvesting Chaeto. It's not easy to remove nutrients by harvesting part of a DSB. I would rather inefficiently remove nutrients rather than efficiently (?) sequestering them in a DSB.

Part of my bias is from moving tanks with a DSB. The amount of waste and the disgusting smell (scientific term ) is overwhelming once the tank is drained down and the LR is removed imho. Or to quote my wife, "Get that stinky tank out of our house."

 

[sjm817]

I wouldn't run a DSB in a display. How about the setup that I'm trying? Its a RDSB/fuge. It has no LR, just sand and macro. Its fed off a T in the return pump. The water that is fed to it has already been filtered by filter socks, and has been skimmed. There wont be raw fish poo and food sent to the fuge. It is pretty clean before it gets there.

I know DSB is one of "those" subjects. Is it not true that denitrification happens in a DSB?

 

[snorvich]

I run a remote deep sand bed and a multizonal refugium. I also use ozone. Seems to work pretty well for me in terms of nutrient conversion (RDSB), nutrient export (cheato). My skimmer seems to do well with ozone but I run it through a reactor not through the skimmer.

 

[Logzor]

I do not know much about RDSB but I do have experience with chaeto.

I believe that in tank chaeto is extremely effective. I have this hypothesis because PO4 is hard to measure in the water, therefore, if your chaeto is in a sump it could not possibly take out that much.

If it is in tank, next to your rock, sand, and decaying matter, it can much more effectively capture PO4 leeching from these sources when they are in extremely close proximity.

This has been affective in controlling Dictyota algae in my tank.

Correct me if my hypothesis is wrong or if there is some other theory that makes in sump chaeto more efficient.

 

[LockeOak]

I use skimming, PO4 reactor, a chaeto refugium and a RDSB. The chaeto is really more for pod production than anything else, though any nitrates, phosphates or metals it removes is great too. If you have any kind of significant flow I don't think proximity to the rock or sand would make any difference, once the tank is cycled I would imagine most of the phosphates are coming from food input.

 

[Randy Holmes-Farley]

I have this hypothesis because PO4 is hard to measure in the water, therefore, if your chaeto is in a sump it could not possibly take out that much.

Just because you cannot measure it does not mean the Chaetomorpha is not getting a lot. By definition, if it is growing it must be getting a lot of phosphate.

Unless the macroalgae in the tank is getting phosphate from the substrate with roots or something, there is little difference between in tank and in sump./refugium as the concentrations will quickly equilibrate, assuming you have reasonable flow.

 

[Logzor]

Hmmm. Percentage wise, off hand, do you know how much PO4 is in the "diet" of chaeto?

 

[Randy Holmes-Farley]

I show in this article how much phosphate is present by weight in macroalgae:

Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php

from it:

Phosphate Export by Organisms: Macroalgae



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Growing and harvesting macroalgae can be a very effective way to reduce phosphate levels (along with other nutrients) in reef aquaria. In my reef system, where I have large, lit refugia to grow the macroalgae Caulerpa racemosa and Chaetomorpha sp., these algae are clearly the largest phosphate export mechanisms. Aquaria with large amounts of thriving macroalgae can avoid microalgae problems or excessive phosphate levels that might inhibit coral calcification. Whether the reduction in phosphate is the cause of the microalgae reduction is not obvious; other nutrients can also become limiting. But to reef aquarists with a severe microalgae problem, the exact mechanism may make no difference. If rapidly growing macroalgae absorb enough phosphorus to keep the orthophosphate concentrations in the water column acceptably low, and at the same time keep microalgae under control, most reefkeepers will be satisfied.

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 nine different species of macroalgae, including many that reefkeepers typically maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08 % phosphorus by dry weight and 5.6% nitrogen. Harvesting 10 grams (dry weight) of this macroalgae from an aquarium would be the equivalent of removing 24 mg of phosphate from the water column. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67-gallon aquarium. All of the other species tested gave similar results (plus or minus a factor of two). Interestingly, using the same paper's nitrogen data, this would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same 67-gallon aquarium.

 

[Randy Holmes-Farley]

Here's the linked article referred to above that gives data for many different species:

http://www.botany.hawaii.edu/Bot482/Kaneohe Bay algae N-P Larned Mar Biol.pdf

 

[JNye]

Randy, why 24/7 on the fuge. i thought that photosynthesis needed that break?(nighttime)

 

[Randy Holmes-Farley]

I speculated in an article that there might be benefits from having a dark cycle, if only for reduced electric bills, but when I tried it I saw no advantage and possibly less growth. I think many folks use 24/7.

I discussed it here:

Photosynthesis and the Reef Aquarium Part I: Carbon Sources
http://reefkeeping.com/issues/2006-10/rhf/index.php


from it:

http://reefkeeping.com/issues/2006-10/rhf/index.php#13

Photosynthesis of Algae in Continuous Light vs. Light/Dark Cycles



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Interestingly, three marine microalgae, Skeletonema costatum, Phaeocystis globosa and Emiliania huxleyi,24 were studied for their rates of photosynthesis and carbon uptake mechanisms in continuous light vs. those same species in light/dark cycles (12 h on/12 h off and 16 h on/8 h off). The rates of photosynthesis were nearly twice as high with light/dark cycles as with continuous lighting. In two of the species (S. costatum and E. huxleyi), but not the third, the contribution of bicarbonate to the total carbon uptake increased dramatically in light/dark cycles compared to continuous light.

How this result might relate to growth and nutrient uptake in lit refugia where macroalgae are often grown to export nutrients is not known. However, it is a sign that perhaps continuous light is not optimal, in addition to being more expensive.

 

[Agu]

However, it is a sign that perhaps continuous light is not optimal, in addition to being more expensive.

Just thought this was worth repeating. Although 24/7 light cycles are promoted it's counter intuitive based on the natural cycles of most life forms.

 

[sjm817]

I'm doing some more reading and wonder now if i made a mistake.

To review the setup, its a 180G, 75G sump and just added a 65G 36Lx18Wx24T fuge. Its fed off the return which is "clean" water which has been mechanically filtered and skimmed. It drains back to the sump. There is 9" of playsand and Chaeto which is lit on a reverese cycle.

The idea was from the RDSB threads and the denitrification benefits (are there any)?

I'm thinking the DSB part of this is not worth the effort. This is in place for nutrient export. If pods and such are growing in there, great, but that is not the primary purpose.

Would I get better results by removing the DSB and just running all macro? I can remove the 300# of sand (ugh, not fun), but whatever would work best.

 

[liveforphysics]

Chaeto can not grow without a minimum redfield ratio of about 1:25 P:N respectively.

Like Randy said, if the chaeto is increasing bio-mass, it is inherently removing P from the water.

Also, for be to always test below the range of your kit, that must mean something is removing it, as everytime you feed, you directly add P. All foods we feed add P, reguardless if it says "no PO4", we are still adding P, and at some lower energy level it will become PO4 (or some other P compound).

I've been using chaeto as my sole nutrient export for years. I do not think that NNR in a DSB is actaully results in anything being removed from the system, only moved to a lower enthalpy state, and held in bio or other forms. In other words, it's like putting a garbage can in your house and filling it up. Great for keeping garbage out of the rest of your house, but doesn't really remove garbage from your house until you physically remove the can and dump it.

Chaeto on the other hand is like having maids come into your house, pickup all your available N and P trash, and shove it into a backpack. When you kick the maids out by grabbing a pile of chaeto and discarding, you remove the N garbage from your system with them.

I charted growth rates by weighing clumps of chaeto after spinning it dry in a salid spinner. The chaeto was then placed into enviroments with aproximately equal water flow and equal available nutrient concentration (same water in my reef). I would measure the salad spun dry mass after 0.5weeks, 1 week, 1.5week, and 2 weeks. My research was to test which lighting grew chaeto the fastest (turns out HPS is best, and uses the least power and has the cheapest bulbs), but I made an additional discovery. I found that a photo period of 6hrs produced no less growth than a photo period of 18hrs, yet a photo period of 24hr hours made a small increase in growth rate (but outside of my estimated margin for error).

Also, if the effects on pH are an indicator of growing for an algae, I found by looking at my pH logs that after the first 5-6hrs of the display lights off, and the fuge lights on, that pH began to drop as if my fuge lights were not on.

This inspired me to use a simple solution. 2 fuges, each with a 70w HPS lamp. My display photo-period is 12hrs on 12hrs off. My fuge photo period goes 6hrs on for fuge1, then 6hrs on for fuge2. Now my pH stays solid through the night, and the rate I export chaeto is pretty massive. Aproximately a 3-4X mass increase rate weekly. I estimate I produce about 15-25 gal of chaeto by volume on a monthly basis.

Sometimes I actaully think my tank is going to go into nutrient starvation... I look at the mass of food entering the tank, and even if that food is pure N and P, it boggles my mind that it can produce the quanities of chaeto that it does.

Naturally, other forms of algae have a very hard time growing.

Best Wishes,
-Luke

 

[Chris2500DK]

Luke, with that massive nutrient export from the chaeto, do you run a skimmer as well?

 

[liveforphysics]

Stopped skimming a few years ago.

People think I'm nuts, but I think due to the nature of skimming only being able to remove hydrophobic compounds, I don't think it's capable of a ballanced nutrient export.

I think the ballance of the N in your nutrient export matching the ballance of N you add is important to prevent accumulation of certian ions at undesired levels.

Essentially, while skimming I could never get P undectable without intervention like Ferric Oxide binders.

With no skimming, I easily maintain unmeasureable N and P levels.

That said, I am thinking about making a super-skimmer, but only to have a VERY low water through flow rate. Perhaps 0.1xtank volume per day.

Best Wishes.
-Luke