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Discussion Starter · #1 ·
I know I know, we don't use filters anymore for our tanks. the LR and the sand do that for us. I am a pool and spa guy and I know some people use DE (Diatomasus Earth) for polishing their water. But we also use sand filters in pools and spas. This is about 50 to 200 pounds of sand that the water is pushed through. Has anyobne tried this or would it increase the bad stuff like bio balls??
 

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I think it would be like the bio balls after time. Canister filters with carbon are not bad if you keep them clean.
 

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fluidized sand filters are not that common in SW systems. they are not quite as bad as bio-balls. they collect detritus and clog fairly regularly, so if do not mind regular replacement of the sand than you could use one. unlike bio-balls the sand is never exposed to air, so they will not lead to increased nitrate levels.

G~
 

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Geoff said:
fluidized sand filters are not that common in SW systems. they are not quite as bad as bio-balls. they collect detritus and clog fairly regularly, so if do not mind regular replacement of the sand than you could use one. unlike bio-balls the sand is never exposed to air, so they will not lead to increased nitrate levels.

G~
Actually, fluidized sand filters are much like the top layer of sand in an undergravel filter, although it is not as bad as a wet/dry (the reference to the bioballs), it will still be primarily an oxic (oxygenated) media bed due to the upflow of oxygenated water through the sand, and will produce nitrates, although not nearly as much as would a wet/dry bed of bioballs (due to the relative drop in availability of rate-limiting oxygen in SW compared to atmospheric O2). I dunno what the actual rate of nitrate production would be, but the other issues Geoff mentions would alone be factors in deciding against using a fluidized sandbed for a reef-centered tank. Phosphates will definitely saturate the surface of a calcium-based sand (aragonite or calcite sands), and the issues with silicates in terrestrial organosilicates and gneiss-sourced sands would be issues with diatom blooms, as the tumbling action of the fluidized bed would maximize any dissolution factors associated with these silicate-based sands (although I still do not know if the rate of dissolution would be high enough to trigger diatom blooms)


Just expanding on Geoff's comments, HTH.
 

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sorry, minor hijack here. :D

Tom- i thought that as long as the surface is completely submerged at all times the bacteria are able to create the microenvironment they need for denitrification. i was thinking the fluidized bed would not be that much different than the high energy LR systems we are now creating in our systems.

G~
 

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All I know, is when I use my canister filter, my water quality improves dramatically. The water is very clean, and the livestock seems much happier.
 

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Geoff said:
i thought that as long as the surface is completely submerged at all times the bacteria are able to create the microenvironment they need for denitrification. i was thinking the fluidized bed would not be that much different than the high energy LR systems we are now creating in our systems.
Much will depend on rate-dependant reactions and mechanisms of oxygen consumption within the sand medium environment, even the populations and speciation of specific bacteria driven by the presence (or relative absence) of oxygen, the relative amounts of nitrogen and phosphorus, even the presence and/or absence of light (THIS MAY BE A LARGER FACTOR THAN THE PRESENCE OF OXYGEN, as it may determine both O2 concentration via competative metabolisms by autophototrophs and the relative availability of carbon that may drive O2 consumption by heterotrophs, which will subsequently also affect O2 levels :rolleyes: ) ...kind of a vicious circle of cause and effect that most likely could only be accurately determined by experimentation under a set of specific circumstances. Anything else is random speculation (although we do have the example of undergravel filters to fall back on).

Live rock has both the environments of oxic and anoxic areas forming oxygen gradients to totally anaerobic environments allowing for the localization of these two different metabolic environments in close proximity to each other (and allowing for oxic denitrifications as well), wheras fluidized sandbeds remain as oxic environments due to the continuous upwelling of fresh oxygenated water from the bottom up. I imagine that you could theoretically build a fluidized sand filter deep enough to create an oxygen gradient, but that would be in opposition to the definition of the fluidized sand filter as an oxic environment for deammonification.


I imagine much of the delineation will depend on how we define these filters.
 

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lizzie said:
All I know, is when I use my canister filter, my water quality improves dramatically. The water is very clean, and the livestock seems much happier.
Several different concepts being discussed here: Sand filters that are the equivalent of undergravel filters, physical filitration using a very fine insoluble filtrate in a mat (diatomaceous earth, which btw, are dead diatom silicate tests, the very thing we remove from our water column when we first cycle through the diatom blooms), fluidized sand filters, cannister filters that are usually particulate filters using either paper or similar fine fiber meshes (floss) and carbon, and biological filters based on bioballs (or other wet air-infused substrates) that may or may not have a prefilter for particulates. So we have all three major types of filtration listed here: Physical (particulate) filtration, Chemical filtration (carbon), and Biological filtration (for ammonia and nitrates).

When we say our water is clear and sparkling, we are saying that the water is clear of particulates, and to some extent, clear of dissolved organics like Gelbstoff, so we speak primarily of physical filtrtion, or water polishing, and to a small extent, chemical filtration to remove things like leaky substances from macroalgae and dissolved mucus, etc and the "thaw" from frozen foods, etc. This is usually the particulate materials that we want to remove from the water coumn to make it clear, and we do this by forcing the water through media that 'strains" the particulates out, and physically remove this suspended material. This is the role of the paper filters, floss, polyester filter mats, diatomadceous earth, and physical barrier sand filters. These are the filters that we force the water through very small holes in our filter media to remove floating substances. We for the most part have moved away from this type of filtration in reef systems to increase the diversity of food stuffs available for our filter feeders, including fan worms, bivalves, misc. benthic creatures, and many corals.


The green or yellow tint that many tanks exhibit when looking through the length of a tank is the result of dissolved organics, mainly materials leaked from macroalgae, but also including the soup of many excretions of the life forms in the tank. These substances may be part of an entire food chain, but due to their content of nitrogenous and phosphate bearing substances, are often removed from closed systems to prevent the decomposition and subsequent release of free nitrates and phosphates into a system's food chains. This release often results in nuisance algal blooms if allowed to accumulate to levels that will trigger these blooms. Most often we seek to remove these substances by skimming, which, I guess in reality is a physical filtration, as it DOES depend on a physical removal based on the physics of the air/water interface; but also on chemical filtration via the use of substances like Granular Active Carbon (GAC), resins (Chemipure), Granular Ferric Hydroxide (GFH=Rowaphos, Phosban), exchange powders (Aluminum Hydroxide= Phosguard) and related substances that either react to form insolube complexes with the substance to be removed, adsorb the substance to its surface, or exchange ions to insolube resins to ioniclly bond with the substance being removed. These methods of chemical filtration have a limit, and if this limit ix exceeded, may allow for the re-release of these substances bak into the wawter column as they are metawbolized by bacteria that colonize the surface of these substrates.



The type of filtration we often attribute to the bioballs, live rock, live sand, and any substrate on which bacteria can grow and multiply is biological filtration. It is the reason we can keep captive reef systems without having readily available 100% seawater changes for our systems. The bacteria are responsible for the mineralization of ammonia to nitrate. Through the many food cycles within the bacterial biotope, they also account for cycles for phosphate, nitrate, sulfur, and carbon. When we speak of the other types of filtration, we usually do not think of them as biological filtration mechanisms, but it is the very presence of these forms of filtration that often lead to biological filtration centers of activity. When filter floss (or for that matter, GAC, and in a fluidized or physical sand filter the sand granules themselves) become loaded with particulates, the bacteria are then able to colonize these substrates (as that is what the filters then become). These bacteria begin to break down the undigested or uneaten particles, even the poop of fishes, etc, into their constituent components, making these particulate filters biological fiters. Although this may seem like a good thing (heh, a self-cleaning filter!), it is this very decomposition of these filtrates that creates the most difficult to remove substances in our aquaria: totally dissolved nitrates, phosphates, and small carbon fragments (DOC's). The mechanisms of how this occurs are detailed in many threads on the net, some more accurately than others. Rather than go into the specifics, I would suggest that you read The Microbiological Ecology of the Ocean. edited by David L. Kirchman. There is an entire chapter on the subject, and it has several chapters that deal specifically with nitrification and the marine nitrogen cycle, the food cycle of autotrophic vs. heterotrophic bacteria, and the symbiosis and mixotrophy that occurs in cycling nutrients within this food web. The upshot of what you should get from our discussion here is that many of the physial filters that we could employ in keeping marine aquarium water spwarkling often result in the release of nutrients into the water column in their most difficult to remove form, something that we need to balance with our need for sparkling clear water when we consider using these methods of filtration.


Sorry to ramble on like this, I was totally carried away...

 

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Discussion Starter · #9 ·
Ok Ok I am just a mere Spa fixer. Plain english.....Good idea, Bad Idea

BTW 200 gal glass tank some fish some softies and a couple anenome, 100 maybe 150 lbs LR 2-4 inches of sand depending on where they decide to move it this week
 

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TahoeMtn said:
Plain english.....Good idea, Bad Idea

BTW 200 gal glass tank some fish some softies and a couple anenome, 100 maybe 150 lbs LR 2-4 inches of sand depending on where they decide to move it this week
prolly for the tank in question, it is a non-issue, although I would personally want to leave the suspended material in the water for the filter feeders. Prolly enough just to run a good skimmer, have sufficcient live rock, and run GAC 24/7 in the system. If you feel you need more than that, run a cannister once a week with a paper filter and about 2 cups of extra carbon for 24 hours, then pull it and clean the filter in prepertin for the next needed water polishing. It wouldn't hurt to run a snd filter, I just dont think it would help as much as you might imagine, although it will get the water clean.
 

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Tom, what do you do for a living? My god, your familiarity with this is at an incredibly intellectual level!!! I'm impressed!
 

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Heh!

Alice and Doug taught me everything I know.

:D
 
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