Questions regarding your article...

[monkeyboy]

Aquariums with no plenum can achieve denitrification in a thinner layer of fine sand, but it is not as effective as a thicker layer of coarse gravel over a plenum, and the fine sand method has a higher risk of developing hydrogen sulfide gas (which kills fish rapidly)

Then you later go on to say...

A surface skimming overflow insures sufficient gas exchange to keep the oxygen from falling too low, and rapidly causes an off-gassing of any hydrogen sulfide.

So if an aquarium is equipped with a surface skimmer, there's no need to worry about hydrogen sulfate from a DSLB (or in this case a thin live sand bed)? (I personally don't, even in tanks w/out surface skimmers.)

Sometimes phosphate and silicate levels are elevated in the plenum as well (J. C. Delbeek, personal communication). However, the levels do not stay high, and the plenum water does not cause sudden fluctuations in the water quality of the aquarium, as has been suggested by some authors

So, where do you figure they go? They must go somewhere. I would conjecture that these elevated levels are a result of using a gravel bed, where the detritus is just sitting there being broken down by bacteria. One of the pro's of a DLSB is that the proliferation of worms and some crustaceans keep this stuff moving back into body mass then back to the fish as they eat some of the critters or their spawn. Dr. Shimek and various other authors have proposed that a gravel substrate is not optimal for the proliferation of worms which would make the plenum a detritus trap more or less. What are your thoughts on this? And where is the excess silicate coming from? Seems to me that this would be caused by the decomposition of fecal pellets of herbivores which have consumed diatoms, which is where a sizable amount of the silicate in the aquarium is located. If this is so, then it would concur with the belief that the plenumis mainly trapping detritus and not processing it quickly enough. What do you think?

Not trying to turn this into a DLSB vs. plenum debate but there's still a lot of mystery about how plenums work (or if they even do!?).

Thanks!
Kevin

 

[monkeyboy]

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