Experimental Comparison of Sandbed and Plenum-Based System

[reef]

An Experimental Comparison of Sandbed and Plenum-Based Systems: Part 2: Live Animal Experiments

http://www.advancedaquarist.com/2005/7/aafeature

[wasp]

Hmmm... Very interesting. I can remember this debate raging a few years back, everybody had strong opinions.

I think it's a little academic now though, as time has shown that neither system will give pristine water quality for the long haul, although just depends how a person manages their tank and what they want and do.

[lduncan]

So true. Both systems have the same major flaw, which make them less than ideal for setting up a tank.

Layton

[Fay]

It's all over my head

[RnB]

Overall Summary:

Our experiment shows no evidence for any of the espoused benefits of a plenum (reviewed by Goemans 1999) either with or without live animals in the design. Instead our results suggest that any benefits seen are a direct consequence of the presence of the sediments themselves rather than the void space beneath it.

Each sediment-based aquarium design appeared capable of handling nutrient inputs up to 0.5 mg / L / day of NH4+ - which is equivalent to a well-stocked reef aquarium. At this input level, final concentrations of ammonia, nitrite and nitrate did not differ significantly among aquaria 1) with or without plenums, 2) containing deep (9.0 cm) or shallow (2.5cm) sediments, or 3) containing coarse (2.0mm) or fine (0.2mm) mean particle sizes. Bioload and animal deaths in the aquarium show a much greater effect on the water quality than does the specific design for the tank.

The greatest differences among experimental treatments were observed as decreased buffering capacity, and higher final phosphate concentration of aquaria with coarse sediments relative to those with fine sediments. However, the chemical composition of the gravel may be responsible for this effect, and we have not tested other gravel types of similar size. We recommend that aquarists test any new gravel for dissolution before adding a lot of it to their aquarium.

We show that there can be extreme variation among identical tanks, even without any live animals included as outlined in Part 1. Given the added variability as soon as live animals are included into the mix, our results highlight the problem with drawing any conclusions based on a single aquarium - no matter how beautiful it may be. The results from any study lacking proper replication and controls should be viewed with suspicion. We argue that anecdotal evidence is simply presentation of an opinion in cases such as this, and more than 5 years of heated debate on the merits of DSB vs. plenum systems has resulted from the staunch defense of opinions without data.

We show that even high-quality aquarium tests provide only a ballpark estimate of the actual concentration of nutrients in the aquarium. However the readings from the Salifert test kits were sufficiently correlated with the true nutrient values to be reliable for comparisons among aquaria.

Overall death rates were roughly twice as high in aquaria with shallow sediments as in deep sediment treatments. The highest overall death rates were seen in aquaria with shallow coarse sediments over a plenum, and the lowest death rates occurred in aquaria with a sandbed composed of deep coarse sediments. The treatments that were closest to the design aquarists employ for deep sandbed, Miracle Mud and Jaubert plenum aquaria had intermediate death rates. The shallow coarse sediment design that is closest to that used in Berlin systems had one of the highest death rates, and the deep coarse sediment design for which there is currently no accepted name had the lowest overall mortality (Fig. 10). We did not test bare bottom tanks, but the data clearly suggest that the shallower the sediment, the higher the mortality rate, and you can't get much shallower than a bare bottom tank!

Experimental results were surprisingly similar between the aquarium dosing and live animal experiments. Contrary to our expectations, the presence of live animals and sediment infauna does not have any measurable effect on final nutrient concentrations in our experimental aquaria.