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Paul Auger, "The Quantitative Comparison of Two Nutrient Removal Systems"; August 15th, 1999 on #reefs...

The Quantitative Comparison of Two Nutrient Removal Systems

Paul Auger

August 15th, 1999 on #reefs

Paul Auger is currently working at the Chesapeake Biological Laboratory as a nutrient chemist. He graduated from St. Mary's College of Maryland with a Bachelors of Science in Biology and for his senior thesis he completed research on the comparison of two nutrient removal systems. He also participated in the construction and stocking of the laboratories marine facilities. Paul has been fish keeping for the past 12 years, marine for the past 6, and reef for the past 5. Paul has had several different reefs, the most recent is his 45 gallon.

The Quantitative Comparison of Two Nutrient Removal Systems

The following is a summary of a one-year research project conducted at St. Mary’s College of Maryland in St. Mary’s City, Md. The study consisted of three 6-week surveys of two identical 250gal recirculating seawater systems. Each system was stocked identically with live rock, corals, fish, and sea urchins. The only variance between the systems was the means of nutrient removal. System one was a deep plenumed sand bed. The plenums were added specifically to allow for inter-bed water sampling. System two was a Berlin style system, which utilized an ETS 1000 clone.


The purpose of this experiment is to determine which method of nutrient removal is best suited for long-term use in recirculating marine mesocosms. There are many ecological risks associated with keeping mesocosms, to both the organisms and the reefkeeper. But the most prevalent of all concerns is eutrophication. Eutrophication can be caused by many factors including overfeeding, overloading of system, poor make-up water, and poor system maintenance. Such eutrophic conditions can lead to meager health, frequent disease, and untimely death of the systems inhabitants. The maintenance of natural chemical, biological, and physical parameters within the laboratory and the home aquaria is essential for organisms well being.

This project focused on the removal capacities of each system. Data will be presented graphically to help illustrate the similarities and differences found between each system. Nutrient exports are the basis for most analysis. Because all variables are controlled and equal between tanks, nutrient concentrations can be compared to each other over time.

System Setup:

Tank Description: The systems followed a two tray design, the top tray was where the organisms were contained and the bottom tray acted as a sump/sand bed for the respective systems. The overall dimensions of the trays were as follows:

Top Tray- 97.5cm L x 13.4cm H x 67.8cm W = 89L

Bottom Tray- 97.5cm L x 60cm H x 67.8cm W = 397L

Two predrilled 10gal tanks were attached to each system with flow through apparatus to provide housing for the fish and urchins. Water circulation was provided for each system via one Iwaki 45rlt. Water top off was supplied through an automatic water addition system. Total volume of RODI used was measured for each trial. No water changes were performed over the course of a specific trial run. RO/DI used was 18megohm lab grade water. All seawater was made up using Instant Ocean salt mix to 36ppt verified with a pre-calibrated Licor refractometer. Lighting was provided for each system by one Hamilton Reefsun metal halide light fixture. Each fixture contained two 175watt 10000K metal halide bulbs.

Live Rock (LR) - The LR used within this study was collected from Marathon Key, Florida. Two hundred pounds of LR was added to each tank after being transported and cured.

Coral - Species one: Sarcophyton sp. was purchased from a local supplier and was collected in Fiji. After acclimation it was divided into 16 sections, eight were placed into system one and eight were placed into system two.
Species two: Porites sp. was collected from Marathon Key, Florida. Five full sized colonies were collected and transported. After acclimation 16 smaller colonies were established and split, 8 into system one and eight into system two.

Fish- Fundulus heteroclitus were collected from the St. Mary’s River, Maryland. One hundred and fifty grams of fish was placed into each system and fed daily to promote overfeeding and nutrient input.

Sea Urchins- Litochinous sp. were purchased from a Florida based marine life collector and shipped. Once acclimated, four equal sized specimens were placed into each system.

Sand- 400lbs of Florida beach sand and crushed coral was collected from Marathon Key, Florida for use in system one.

Physical Parameters:

The systems were monitored twice daily for the following physical parameters: pH, redox potential, dissolved oxygen, temperature, salinity, food added.

Sand Bed description: The sand was collected, packed into two 40 gallon Rubbermaid trashcans and transported moist. It was then sifted for grain size and distribution within the sand bed. The plenum depths and sand depths were as follows:

----------------------top layer
2" sand
----------------------plenum 1
3" sand
----------------------plenum 2
2" sand
----------------------plenum 3

Each plenum was 2" deep allowing for just enough room for sampling. The sampling was performed via closed and sealed valves that were circulated via small mixing pumps. The probes were placed in-line and sealed for sampling purposes. Dissolved oxygen and redox potential were measured via probes. Nitrate, nitrite, phosphate, and hydrogen sulfide were measured through direct sampling using sediment sampling techniques described in the Standard Methods of Water and Wastewater Analysis Handbook.

Foam Fractionator: The overall dimensions of the foam fractionator were as follows: Height - 69cm, diameter - 14.5cm, box length - 40cm, box width - 30cm, box height - 40cm. The fractionator was run via an Iwaki 1000rlt through a 747cm downdraft tube. The skimmer produced approximately 10L of skimmate over each 6week trial.

Analytical methods:

All nutrient analysis was completed using a Hach DR 3000 Spectrophotometer. Ammonia was tested using the Hach salicylate method #8155. Nitrate was measured utilizing the Hach cadmium reduction method, #8192. Nitrite was measured using the Hach diazotization method, #8507. Orthophosphate was measured using the Hach ascorbic acid method, #8048. Hydrogen Sulfide was measured via the Hach Methylene Blue method #8131.

Data and Conclusions:

Samples were collected weekly for nutrient analysis at corresponding times from zero. Each sample was run in triplicate and the appropriate concentrations were obtained via a regression analysis. After all raw data points were collected, each nutrient data set was combined via each trial (x=3) and analyzed for variance from time zero. Each data set showed no significant variation between trials and was thus averaged for each measurement to give an averaged data value over time for each nutrient. In easier terms, all the data for ammonia day 0, trials 1,2, &3, were combined and averaged to give one data point, this was then done for each nutrient at each interval from zero.

Table 1 shows cumulative data from all three trials, averaged and plotted according to time from day zero. Graphical representations of each nutrient can be found at the following: Ammonia

A quick summary of the graphs for those of you who can't view them- The ammonia graph shows no true variance over time between each system. The Nitrate graph shows a general upward trend, however the Berlin system rockets past the sand bed approximately half way through the trial. The Nitrite graph is similar to the ammonia graph. The table shows low oxygen level, low redox potentials, all corresponding to those conditions needed for a good sand bed. However, the nutrient data for the sand bed shows a slightly different value. In these graphs one can see the low nitrate, nitrite and hydrogen sulfide values. All of which are good news. However, the high phosphate values are worrisome. This data shows one particular anomaly, higher than normal levels of phosphate. One would typically expect to see some phosphate within the sediment area, but concentrations as high as those found within the bed are peculiar.

They actually raise more questions than answers. This I believe is likely to open up more debate and until a more long term and comprehensive study of such a topic is accomplished, will remain a topic of concern and debate.


American Waterworks Association. 1992. Standard Methods for Water and Wastewater Analysis, Eighteenth ed.
Brower, Zar, and von Ende. 1990. Field and Laboratory Methods for General Ecology, Third ed. Wm. C. Brown Publishing.
The Hach Company. 1995. Water Analysis Handbook. Hach Company.


I would like to thank Dr. Walter I Hatch and Dr. Beth C Colburn for all their help on this research. I would like to especially thank Margot Kopera for all her support and understanding during my 18 hour days and no sleep nights.

That is it....any questions?

I just think I missed this, but did both systems have an identical skimmer, or did Berlin only have a skimmer?
Only the Berlin- it had the ETS clone.

Did you use kalkwasser top off in each system, if so how much a day?
No, we only dosed initially. Part of the study that did not work out was trace removal. I left that out because of the poor correlations and results.

Did you say that you used beach sand? If so, isn't that dangerous for the system?
It was collected, transported and then rinsed/sifted. All organic materials were removed. Other than that, I feel that there is really no harm in using beach sand.

Why not test several smaller tanks instead two large tanks? This would replicate the experiment several times just as your testing of water parameters in triplicate removed any error?
That was an idea that came to me after the beginning of the second trial. I guess just bad timing. It was also due to the old... what was there is what I could use. I received no money, everything was done out of pocket, so I really was forced to use the sytems that were there.

Can you briefly describe a "Berlin" system to be to make sure we're all thinking of the same type of system?
It is a typical skimmer and live rock system. Large skimmer, heavy skimming, live rock for denitrification.

I gather that the Berlin system had no sand at all. Do you think that the lower nutrient levels in the NNR system could be because the sand was acting as a big nutrient sponge, rather than somehow processing or "removing" the nutrients? It would be interesting to see what happens after three years rather than three weeks...
Very true. I believe that the only nutrient being sponged was the phosphate. This opens up a whole line of debate. But the data points to no nitrogen sponging. I feel that in some instances the sand could be a sponge, and in that I feel that depth plays an important role. I don't think that we know enough as of yet to really understand how the full nutrient cycle works in our enclosed systems.

Was that data collected from the sediment or the water column, and if from the sediment, what "sediment" was tested on the Berlin?
There was water column testing for each system. There was also sediment collection on the NNR system. This was done to monitor the bed- it was really for kicks at first but in the end turned out to be very interesting.

How can samples be taken from the plenumed system w/o allowing oxygen to penetrate the bed along with the sampling device?
We had the system preplumbed and sealed. Each probe and the ensuing sediment sampler was sealed into place for sampling. The method for water removal from a sediment core is easy with the right equipment which is really what we used. It was a needle aparatus into a sealed and prefit entranceway.

Do you feel that testing water in the plenum is equivalent to testing water within the sandbed itself?
Not exactly. But with the technology constraints upon us.... we had to make due. I feel that the sand bed is somewhat different due to the particluate - water interactions within the bed. I feel that a true sediment sample would have been more convincing but at the point in time unrealistic.

In the ANOVA model for stats, what error terms did you introduce?
I used an alpha of 0.05... Other than that im not exactly sure what you mean by error terms.

What makes you say there was no evidence of nitrates being sponged, yet you think phosphates were?
The nitrogen composition of the plenum water was at or below in most cases the detection limit of the method. Whereas the phosphate levels were well above the limits and actually above those concentrations found within the water column itself. I believe the phosphates were due to their enormously obvious presence. No where else within the system were such high concentrations of phosphate. Thus it would point to a sponging effect of sorts in the plenum.

Do you think the addition of kalkwasser would have changed the outcome in the plenum? calcium levels within each system were not significantly different.

what did you use for Ca and alk replacement (I may have missed this)?
Nothing, there was no replacement as.... part of the experiment was trace removal over didn't work out.

Were there any macroalgaes in either system? If so were they equal in each?
Yes, there were macros. We had equal wet weights of Thallasia, Gracilaria, and Caulerpa in each system.

Was the sand from the beach (dry/dead) or off the beach (wet-/ive)?
A wet/live - dry/dead mix. I had to spend approximately 10 hrs in the hot sun hauling it up a steep cliff, but it was clean/washed through.

Was any attempt made to measure growth increase in corals and fish to see how livestock faired over the tests?
Yes. Another student sort of leached off my project and photometrcially measured the growth of the corals etc. Again, I never saw that data, but from first hand experience, each of the 8 colonies of each species was the same size as the mother colony by the end of the third trial.

Did you have any die offs of original critters collected, either fish or coral or invert?
Some. Only fish though. The original Fundulus were not acclimated well. They are primarily estuarine fish, which allowed for some die off. All weights were kept constant tho.

Did the macroalgae grow faster in one tank?
No.... not statistically.

What materials were used in construction of the plenum? Typical. Eggcrate, very little mesh screening- that was used to prevent movment of sediment into the water collection areas.

What maintenance will you do to a plenum?
IMHO...Nothing. I feel that a well made sandbed should really deserve little maintenance. The only real problem with a plenum is as the substrate dissolves at the bottom nothing is replaced.

Man, I have to say, I think maintaining a plenum has GOT to be a lot of work. Do you think it's worth it? Doesn't this thing break down after time? When it does, isn't it catastrophic?
I think so..... IMHO it isnt worth it. I believe that if we had the right materials and a little different setup, I would have done this completely differently and not used a plenum.

Do you feel it would have "settled" in better over time?
Hard to say. Constant overloading will kill any filter over time. I do feel that eventually the plenum would have literally fallen apart. I did some calculations to show that at a slow rate of dissolution it would take approximately 10 years to dissolve a 100lb plenum.... if I remember that right.

If the skimmer had been placed on the NNR, a hybrid so to speak, how do you think that would have affected the end results?
I beleive it would have had excellent results. You really would have had the best of both worlds. I think that the water column concentrations for phosphate in the plenum were false. I believe that the total phospahte in the system was relatively higher than the Berlin system. A combo system would radically affect the overall chemistry for the positive.

Does you feel that sand additions over time would allow the plenum to "survive" and thus "thrive"?
...if you could add to the bottom of the plenum, yes. However in this setup that would be impossible. Since there were three separate sections one would not be able to add.

Do you know if plenumed systems are capable of methanogenisis?
I believe that they are.... in my heart of hearts. I think that if the bed, any sand bed, is deep enough a true carbon, nitrogen, and phosphorous cycle can be achieved. I also feel that a sand bed should have a healthy sulfur cycle... just not too healthy.

Did you do any testing of the skimmate to see what exactly was being removed?
Yes. It was interesting, smelly, and difficult. The results were not perfect and were not included here. I do have the data if anyone is interested, I can post it alternatively later on.

Did you go in with any bias? (a preferred system of your own, so to speak)
Not really. Although I came away with one.

With the majority of reef keepers not keeping a TRUE Berlin system but a NNR and skimmer, do you think it is better to go with a NNR or a combo of Berlin/NNR?
Yes. I think that the best system is a truly natural system, not lots of (if any) skimming and a deep sand bed with macrophytic algal growth. But that is not always easy or ideal for a home aquarist.

What made you want to do this extensive work?
A previous experiment on the skimming efficiency of our first ETS clone. A love of chemistry and this damn addicting hobby.

Any idea if this project will be repeated? And maybe a deep sandbed (no plenum) system included in the trials?
No way. Not unless I can convince the college to pay me for it. I did this as my senior thesis. If I could I would do another one.... but the time and energy is way too much for me to work full time and do another one.... So in a nutshell, probably not.

I was curious, would there be any benefit to setting a dual plenum (one plenum over another) in otherwords sand - plenum - sand - plenum?
That was bascially how we did it. I'm not sure how well my diagram worked....but it was really a triplenum. The real advantage to that is the ability to see the true stratification of nitrogen cycling. In a three tiered plenum we could see evidence of oxygen gradients and ammonification, denitrification, and nitrification. It was nice from a scientific standpoint but not from a hobbyist point of view.

I may have missed it, but why only a 35 day trial?
Well....our first run bascially maxed out right around 35 days. We ran a prelim for 60 days and it ran constant after the 35 day mark. So to get replication in we narrowed it down to 35.

What is the status of the two systems today?
Both healthy hybrids. Each churns out enough frags to support the work they are doing now. Right now they are looking at chemical communication between corals, and they are doing more identification work.

How much would an extensive test cost ?
Approximately $1500. I was lucky to scrounge chemicals, space, and instruments. But typically about that much. That of course does not inclued the tanks etc....

Any idea if the ability of the plenum to sponge phosphate would be maxed out eventually? And if so, care to take any guesses as to a time period?
I think that as the calcium substrate becomes overwhelmed the phosphates will start to really max out the plenum. Depends on the system size....maybe 3-5 years.

Would greater circulation have helped the phosphate export?
Probably not as it would have only moved the phosphate into other portions of the bed and back to the plenum. But again, I am hypothesizing on this one. what if there are high pollutant levels in the sandbeds or plenums. The real question is if these affect our tanks, or if they stay in the bed. How can this be measured?
Long-term testing.

Do you have any pictures of what the two tanks looked like?
Yes.... Aquarium Filtration Comparisons From there I believe that you all can find the pics.

Do you think a hybrid plenum/ skimmer combo could deter the failure of a plenum over years?
No.... I think that it can slow the failure but not really stop it. If the plenum is going to fall apart it will fall apart. Again, I believe that if the bed is deep enough, then you can deter such a thing, but not otherwise.

Does this triplenum represent a benefit to the hobbiest or just the scienctist?
Just the scientist. ;-)

OK, last one- Did you learn anything in particular that will change how you would setup a tank in the future, if so what would you change?
Well, I learned that a plenum is not as good as it is hyped up to be. Singular systems are also not truly the way to go. I did learn a lot about benthic dynamics and that they really are probably the most important factor in maintaining you water besides frequent water changes.

Well, that is it for the questions and the formal part of the meeting. Thank you very much Paul for taking the time out to talking to us tonight. It is very much appreciated.

© 1999

Created by liquid
Last modified 2005-02-07 05:53