Tell me about deep sandbeds/ removing mechanical filtration

[duberii]

I'm reading about some reefkeeping methods that are a bit different from what most of us are doing now (this is admittedly stemming from these methods being used in tanks that have been successful with goniopora corals). The first one I heard was a deep sandbed (meaning 4-6 inches from what I've seen). What is it claimed to do (lower nitrates,ammonia, phosphates...?) and what causes that change (growth of what kind of bacteria...?)? How is the surface of the sandbed kept clean- can you still siphon off the top, just being creful not to dig down too deep, or is that one of the downsides of a deep sandbed?

The second one I'm curious about is completely getting rid of filter socks/ mechanical filtration, which was a strange idea for me to hear. I assume there would still be some mechanical filtration in the sense that the chaeto in a refugium tends to collect some particulates over time, but the benefit im seeing is that there is more "food" in the water column for filter feeders (like gonioporas are thought to be).

Here is the article I read- https://reefs.com/magazine/the-successful-aquarium-culture-of-goniopora-species/ (It came out 15 years ago, so I'm not sure how it holds up today) It also suggests very little skimming (dry skimming), which I also think is strange, though I guess if the goal is to keep nutrients in the water column, it makes sense.

If anybody has a tank with any of these methods, tell me about your experience and what changes you have noticed (or not noticed).

 

[garbled]

I'm trying to remember the name of the person who used to promote these alot years ago.. Ron Shmeck? dunno.. Basically the idea is you do not want to vaccum the sand at all. What you want is a huge biodiversity of stuff that crawls around in there and sifts it, but *does not eat the microfauna*. Ie, sand sifting gobies and mandarins are a hard NO. You want the sand to be moved around by worms and pods and whatnot, (nassarius snails are good at this too).

Skimmer is optional, you can run with or without. You could run with socks too. The point is the deep bed denitrifies, and the critters keep it stirred. If you "clean" the sand, you basically wipe out the critter population and make things worse.

I run these on all my tanks. I'm still a fan. It's not the "modern" way, I know that. I don't advocate them because arguments make me break out in hives.

 

[Andrew Zimmerman]

I do not use any mechanical filtration. I just clean the sump once a year. This method has worked for me for years and years. Plus no filter sock cleaning.

 

[duberii]

I'm trying to remember the name of the person who used to promote these alot years ago.. Ron Shmeck? dunno.. Basically the idea is you do not want to vaccum the sand at all. What you want is a huge biodiversity of stuff that crawls around in there and sifts it, but *does not eat the microfauna*. Ie, sand sifting gobies and mandarins are a hard NO. You want the sand to be moved around by worms and pods and whatnot, (nassarius snails are good at this too).

Skimmer is optional, you can run with or without. You could run with socks too. The point is the deep bed denitrifies, and the critters keep it stirred. If you "clean" the sand, you basically wipe out the critter population and make things worse.

I run these on all my tanks. I'm still a fan. It's not the "modern" way, I know that. I don't advocate them because arguments make me break out in hives.

What will stir the sand but doesn't eat the associated critters? I was thinking about possibly adding a sand sifting starfish or some type of sea cucumber, but that seems like those are out of the picture. Nassarius snails are really the only thing I can think of. However, I do think you would need something large turning over the whole sand bed very often, since the stirring is what replaces the need for siphoning off the top layer of detritus, right? I love tanks that are super biodiverse- i love to see all the creatures doing their own thing in a reef (i love seeing people's live rock hauls with hitchhikers and all, and I'm sure something like this will scratch a similar itch).

I'm considering having a DSB for my amphipod breeding tank, but I only have a 10 gallon for that, meaning I would have a shallow water column, and I'm scared that the amphipods might be eaten by other creatures in the tank- who knows.

 

[Pistondog]

No sox for 2 years, except after cleaning refugium for a day.
I agree more food for filter feeders and less work for the lazy.

 

[bam123]

In my extensive experience, DSB are very successful for 2 years and then crash (even with the use of a plenulum). Everyone has different results. I am tempted to try again with the use of an algae scrubber and E-phosphate, but my Barebottom looks great (that's what she said).

 

[garbled]

Cucumbers are generally ok, as they tend to not eat the bugs, but they do sift the sand quite extensively. Starfish on the other hand are bad, as they sift the sand looking for the bugs, so they ruin the bed.

Stuff I use:
Worms (peanut, bristle, spaghetti)
Pods
Nassarius Snails
Conches
Tiger Tail cucumber
Any other snail that digs around really
Pistol shirmp
Fish that dig for caves and stuff, not fish that sift the sand for food
micro brittle stars

Stuff that is known to be bad:
Starfish (specifically the Linkia red/blue type, as they are sandbed predators)
Mandarins
Sand sifting gobies (the kind that eat the sand, tunnelers are ok)

You don't need to grind the sand with some monstrous quantity. It's not like how one would vaccum where the whole thing is turned over at some massive rate. What you are trying to do is basically keep it from solidifying in any way, and have a slow turnover of grains.

You will definitely have a more bio-diverse tank. What you have to get over with this approach is the idea that your sand will be pristine and white. People look at a DSB, and see all the ick against the glass, and the dirty sand, and it offends their sensibilities. I get that, might not be the look you are going for.

As for the crash after a few years, yeah, some people have problems with them. I don't know that I can pinpoint why. I can say that I ran a DSB on my 120 for 3-4 years with no issues, and then moved the tank to a new house, kept the original sand, and it's been running for about 18 years now in it's new home. Every now and then the pod/worm/whatever diversity crashes a bit, and you have to replenish. It's easier if you have 2 tanks and can kind of seed from one another, rather than ordering more stuff off IPSF.

 

[duberii]

Cucumbers are generally ok, as they tend to not eat the bugs, but they do sift the sand quite extensively. Starfish on the other hand are bad, as they sift the sand looking for the bugs, so they ruin the bed.

Stuff I use:
Worms (peanut, bristle, spaghetti)
Pods
Nassarius Snails
Conches
Tiger Tail cucumber
Any other snail that digs around really
Pistol shirmp
Fish that dig for caves and stuff, not fish that sift the sand for food
micro brittle stars

Stuff that is known to be bad:
Starfish (specifically the Linkia red/blue type, as they are sandbed predators)
Mandarins
Sand sifting gobies (the kind that eat the sand, tunnelers are ok)

You don't need to grind the sand with some monstrous quantity. It's not like how one would vaccum where the whole thing is turned over at some massive rate. What you are trying to do is basically keep it from solidifying in any way, and have a slow turnover of grains.

You will definitely have a more bio-diverse tank. What you have to get over with this approach is the idea that your sand will be pristine and white. People look at a DSB, and see all the ick against the glass, and the dirty sand, and it offends their sensibilities. I get that, might not be the look you are going for.

As for the crash after a few years, yeah, some people have problems with them. I don't know that I can pinpoint why. I can say that I ran a DSB on my 120 for 3-4 years with no issues, and then moved the tank to a new house, kept the original sand, and it's been running for about 18 years now in it's new home. Every now and then the pod/worm/whatever diversity crashes a bit, and you have to replenish. It's easier if you have 2 tanks and can kind of seed from one another, rather than ordering more stuff off IPSF.

Interesting- I'd love to get the TBS "package" with live rock and sand, then maybe have a DSB on that system- that would be amazing. Unfortunately, that seems pretty far off, both because of the cost and because I'd have nowhere to put another tank . That is a dream for me, but I'm not sure how trusting I'd be to put corals in that tank (at least expensive ones) because I'd assume predatory worms would be more likely to survive in such a system- maybe that's just an assumption on my part.

I wonder what causes the "crashes"- that seems like a huge downside for me. I wonder if there's anything that can be done to prevent crashing- of course there ill always be fluctuations in the population, but I'd hate to randomly lose critters.

 

[HuduVudu]

I'm reading about some reefkeeping methods that are a bit different from what most of us are doing now (this is admittedly stemming from these methods being used in tanks that have been successful with goniopora corals). The first one I heard was a deep sandbed (meaning 4-6 inches from what I've seen). What is it claimed to do (lower nitrates,ammonia, phosphates...?) and what causes that change (growth of what kind of bacteria...?)? How is the surface of the sandbed kept clean- can you still siphon off the top, just being creful not to dig down too deep, or is that one of the downsides of a deep sandbed?

The second one I'm curious about is completely getting rid of filter socks/ mechanical filtration, which was a strange idea for me to hear. I assume there would still be some mechanical filtration in the sense that the chaeto in a refugium tends to collect some particulates over time, but the benefit im seeing is that there is more "food" in the water column for filter feeders (like gonioporas are thought to be).

Here is the article I read- https://reefs.com/magazine/the-successful-aquarium-culture-of-goniopora-species/ (It came out 15 years ago, so I'm not sure how it holds up today) It also suggests very little skimming (dry skimming), which I also think is strange, though I guess if the goal is to keep nutrients in the water column, it makes sense.

If anybody has a tank with any of these methods, tell me about your experience and what changes you have noticed (or not noticed).

I use a fully natural system on both of my tanks. Here pictures for cred.

I advocate these type of systems they are incredibly stable and the little life is amazing and kewl. My 20 gallon tank used to have a plenum. I was experimenting on making it more effecient and to that affect I added an anaerobic digester. I pulled the plenum for the digester and then when my experimenting ended I pulled the digester. I am breaking down the 20 so I haven't replaced the plenum. I am definitely struggling without it. My new 65 has a plenum in the sump. I have two different gonipora in my 20 that I am dealing with trace element issues, but now that I am back on regular water change schedule are starting to do well again. I feed the 20 and the 65 20ml of phyto a day. My 20 runs at about 5ppm nitrate and about .01 phosphate. My 65 runs about 25ppm nitrate and I have yet to test the phosphate.

Neither of my tanks use any kind of mechanical filtration including skimmers. I think that filtration is a dead end and too many people think of aquariums as waste water treatment plants and not as an anarchic system of interconnected food webs.

Ok, I have had plenums on pretty much every tank I have owned. Also the anaerobic digester taught me a ton about how to best set up anaerobic type of systems. First off on deep sand beds and plenums, I 100% do not advocate using them in the DT. I did use a plenum in my 20 because I didn't have sump. However, the plenum was in a 4 inch pipe with nothing on top. Here is a picture.

The plenum was the thing with hair algae on it. The reason that I did the plenum this way is because IMO you do not want anything on top of the plenum or deep sand bed. These systems are diffusion based and having rock and other things on them creates diffusion shadows. This is very undesireable and IMO the reason most people fail with these systems. On my 65 I have put the plenum in sump. You can see it in the second picture it is in the far left chamber of the sump. Many natural reef aquarists also use reverse flow undergravel filters. These function essentially as plenums but work well in the DT because the flow is going up, not down. The input from the where the lift tubes are can be consistent eliminating the issues of shadows. I have not used these systems but they seem viable to me. One key to them is their low flow. If you might be interested in this type of system look here on R2R or use a search engine. @Paul B uses one.

I do nothing to maintain my plenums. Maybe blow them off, but I don't think about it and it would happen rarely if at all. Plenums do indeed lower nitrates but not phosphates. They however dump a lot of nutrients back into the tank and you can see that in the yellowing of the water. These nutrients feed a lot of low level micro fauna. Yes, that includes algaes. I have many algaes in my tank including dinos and cyano. None can get out of control because they are all fighting each other and other fauna for nutrients. On top of that they are being predated by next teir herbivores. This as it should be. I also found when I used the digester which I fed two balls of hamburger every day (yes it stunk terribly) that hydrogen sulfide plays no role that I could see in the tank.

One benefit most people are unaware of in plenums and DSBs is the minor mineralization that happens. This is pretty significant because it is like a small calcium reactor in your tank. The mineralization isn't much but it supplies a continuous amount of calcium, carbonate and trace elements. In my 20 gallon my porites and stylo were grown from small frags to near their current sizes on a plenum alone, the one in the picture. Were my numbers terrible ... yes, but the corals adjusted and because the amount was continous they were able to grow slowly. This can not be understated as a benefit of these systems.

The food web in these types of tanks are very complex and no human could manage them. My goal in husbandry is to set up a base infrastructure for them to flourish.

Hope this answers some of your questions.

 

[lafarrow]

@HuduVudu (post #9) I love posts like this. Someone is doing something different and takes the time and effort to explain not just what they are doing but why. I also like to see the thought process behind all the choices and the explanation for lessons learned. Finally, a thoughtful discussion of the pros and cons and acknowledgment that what you are doing may not be for everyone. Absolutely wonderful reading this today. Thank you.

 

[duberii]

I use a fully natural system on both of my tanks. Here pictures for cred.

I advocate these type of systems they are incredibly stable and the little life is amazing and kewl. My 20 gallon tank used to have a plenum. I was experimenting on making it more effecient and to that affect I added an anaerobic digester. I pulled the plenum for the digester and then when my experimenting ended I pulled the digester. I am breaking down the 20 so I haven't replaced the plenum. I am definitely struggling without it. My new 65 has a plenum in the sump. I have two different gonipora in my 20 that I am dealing with trace element issues, but now that I am back on regular water change schedule are starting to do well again. I feed the 20 and the 65 20ml of phyto a day. My 20 runs at about 5ppm nitrate and about .01 phosphate. My 65 runs about 25ppm nitrate and I have yet to test the phosphate.

Neither of my tanks use any kind of mechanical filtration including skimmers. I think that filtration is a dead end and too many people think of aquariums as waste water treatment plants and not as an anarchic system of interconnected food webs.

Ok, I have had plenums on pretty much every tank I have owned. Also the anaerobic digester taught me a ton about how to best set up anaerobic type of systems. First off on deep sand beds and plenums, I 100% do not advocate using them in the DT. I did use a plenum in my 20 because I didn't have sump. However, the plenum was in a 4 inch pipe with nothing on top. Here is a picture.

The plenum was the thing with hair algae on it. The reason that I did the plenum this way is because IMO you do not want anything on top of the plenum or deep sand bed. These systems are diffusion based and having rock and other things on them creates diffusion shadows. This is very undesireable and IMO the reason most people fail with these systems. On my 65 I have put the plenum in sump. You can see it in the second picture it is in the far left chamber of the sump. Many natural reef aquarists also use reverse flow undergravel filters. These function essentially as plenums but work well in the DT because the flow is going up, not down. The input from the where the lift tubes are can be consistent eliminating the issues of shadows. I have not used these systems but they seem viable to me. One key to them is their low flow. If you might be interested in this type of system look here on R2R or use a search engine. @Paul B uses one.

I do nothing to maintain my plenums. Maybe blow them off, but I don't think about it and it would happen rarely if at all. Plenums do indeed lower nitrates but not phosphates. They however dump a lot of nutrients back into the tank and you can see that in the yellowing of the water. These nutrients feed a lot of low level micro fauna. Yes, that includes algaes. I have many algaes in my tank including dinos and cyano. None can get out of control because they are all fighting each other and other fauna for nutrients. On top of that they are being predated by next teir herbivores. This as it should be. I also found when I used the digester which I fed two balls of hamburger every day (yes it stunk terribly) that hydrogen sulfide plays no role that I could see in the tank.

One benefit most people are unaware of in plenums and DSBs is the minor mineralization that happens. This is pretty significant because it is like a small calcium reactor in your tank. The mineralization isn't much but it supplies a continuous amount of calcium, carbonate and trace elements. In my 20 gallon my porites and stylo were grown from small frags to near their current sizes on a plenum alone, the one in the picture. Were my numbers terrible ... yes, but the corals adjusted and because the amount was continous they were able to grow slowly. This can not be understated as a benefit of these systems.

The food web in these types of tanks are very complex and no human could manage them. My goal in husbandry is to set up a base infrastructure for them to flourish.

Hope this answers some of your questions.

Thank you so much for the information! I guess this kind of unveiled a significant misunderstanding on my part (and several minor ones). From my understanding, a plenum was pretty much a gap of water underneath the sandbed, but I don't really understand how you are using it- how is that thing you pointed out a plenum, and does it rely on some type of flow going through it? I had also believed that plena (plenums?) were found to be obsolete, but the mineralization could be an added benefit of adding one.

Another understanding I had was that the DSB needed to be directly under the source of the waste (as in under the fish and inverts), since the majority of the solid waste will just sink into the sandbed without being blown into the water column and down an overflow and thus into the refugium with the DSB. The creatures rely on that solid waste (from my undertsanding) which makes a "remote" DSB less effective than a DT DSB.

I believe my sandbed is in a nasty zone between an aesthetic sandbed and a DSB, since it is probably around 2" and accumulates detritus like you wouldn't believe. I'm considering taking the majority of the sand out (possibly to add to a DSB in another tank/in the refugium now that you bring it up), leaving a dusting for aesthetic needs which would be easy enough to clean and siphon.

Now that I mention it though, if what I just said was true, filter socks wouldn't clog up as fast as they do, and my line that empties into the refugium, which doesn;t have a filter sock at the end, wouldn't collect debris... so maybe I just worked out my own misunderstanding.

 

[HuduVudu]

From my understanding, a plenum was pretty much a gap of water underneath the sandbed, but I don't really understand how you are using it- how is that thing you pointed out a plenum, and does it rely on some type of flow going through it? I had also believed that plena (plenums?) were found to be obsolete, but the mineralization could be an added benefit of adding one.

So the theory behind a plenum is that organic waste falls on the top and then goes down through the bed and is anaerobically decomposed and this creates a diffusion gradient that then pulls in new waste and pushes up "clean" water. Jaubert has said in recent years the the dead space was just an old undergravel filter and that he didn't really think it was needed so the DSB was born. This is generally how I see them, but in practice they don't work like the sanitized theory. The theory and practice to agree is that plenums and DSBs work on a diffusion gradient. This means that sand grain sizes are important. I use a two layer approach for my plenums. One thing to note on the dead area I use a very very coarse filter material for the dead area. I have used just space and bio balls in the past but there doesn't seem to be much of a difference between them. On top of that I use a nylon window screen to keep the sand out and then I put a very find silicate sand. This serves two purposes, first it won't break down under acidification and second it ensures a very slow diffusion creating a fully anaerobic layer. On top of this I put a coarser grain calcium carbonate based sand. My theory, right or wrong, is that the upper area is aerobic to anoxic and the lower areas are anaerobic.

Obsolete is a funny word. Plenums/DSBs where used as a way to lower nitrates. They can do this if they are implemented properly, but why would this be neccessary? I don't use them for this reason. I never have. The idea that nitrate and phosphates are the only factors in pest algaes IMO is ridiculous. First off we can only measure what is in the water column and second we have no idea how the food web is dealing with these minerals. I can dose my 20 gallon with nitrate and get the nitrate to 25ppm. Three days later is at 2ppm. Where does it go? Do I see algae growth? ... No. I like to use nitrates as a method for supplemention because I can drive a lot of nitrate to dose trace elements and the nitrate is basically removed leaving the targeted mineral behind. I think that plenums and DSBs supplement the process that is already occuring inside of proper live rock i.e. rock collected from the ocean. I don't think that plenums/DSBs are obsolete I think people have never really understood the role they play and how to best take advantage of them. It is funny because it is like skimmers people think that the Berlin method is the skimmer. It is isn't it is just one piece of the Berlin.

Another understanding I had was that the DSB needed to be directly under the source of the waste (as in under the fish and inverts), since the majority of the solid waste will just sink into the sandbed without being blown into the water column and down an overflow and thus into the refugium with the DSB. The creatures rely on that solid waste (from my undertsanding) which makes a "remote" DSB less effective than a DT DSB.

This is a legit point but from practical experience I haven't see this to be true.

When I start up a plenum, I will squirt frozen food into the first few inches of the gravel (I am trying to get it in the anaerobic area). This seems to make them speed up. Most sumps surface skim and this seems to dump a lot of stuff, but also over time the top of the plenum becomes a biome of it's own. Creatures grow and die there and they all go back to the dust (sand).

Even if this is a consideration, I find the problems of impaired diffusion are far outweighed by having nothing on top of the plenums. Perhaps there could be a way to have one in the DT so that it is bare on top, without being too ugly. Maybe an experiment for another day.

I'm considering taking the majority of the sand out (possibly to add to a DSB in another tank/in the refugium now that you bring it up), leaving a dusting for aesthetic needs which would be easy enough to clean and siphon.

An underrated way of clearing sand beds is to stir them up regularly. I use my hand to do this regularly (maybe monthly or every two months). It is crazy how the water will get all cloudy for a few hours but the next day the tank is brilliantly clear. I also do this hand waving thing to flush the live rock too. I don't think sand plays a super big role in the bed if it is kept under the depth needed for anaerobic decomposition. I am confused by bare bottom tanks, for asthetic reasons but people do what they think is necessary to get their tanks to work.

 

[duberii]

So the theory behind a plenum is that organic waste falls on the top and then goes down through the bed and is anaerobically decomposed and this creates a diffusion gradient that then pulls in new waste and pushes up "clean" water. Jaubert has said in recent years the the dead space was just an old undergravel filter and that he didn't really think it was needed so the DSB was born. This is generally how I see them, but in practice they don't work like the sanitized theory. The theory and practice to agree is that plenums and DSBs work on a diffusion gradient. This means that sand grain sizes are important. I use a two layer approach for my plenums. One thing to note on the dead area I use a very very coarse filter material for the dead area. I have used just space and bio balls in the past but there doesn't seem to be much of a difference between them. On top of that I use a nylon window screen to keep the sand out and then I put a very find silicate sand. This serves two purposes, first it won't break down under acidification and second it ensures a very slow diffusion creating a fully anaerobic layer. On top of this I put a coarser grain calcium carbonate based sand. My theory, right or wrong, is that the upper area is aerobic to anoxic and the lower areas are anaerobic.

Obsolete is a funny word. Plenums/DSBs where used as a way to lower nitrates. They can do this if they are implemented properly, but why would this be neccessary? I don't use them for this reason. I never have. The idea that nitrate and phosphates are the only factors in pest algaes IMO is ridiculous. First off we can only measure what is in the water column and second we have no idea how the food web is dealing with these minerals. I can dose my 20 gallon with nitrate and get the nitrate to 25ppm. Three days later is at 2ppm. Where does it go? Do I see algae growth? ... No. I like to use nitrates as a method for supplemention because I can drive a lot of nitrate to dose trace elements and the nitrate is basically removed leaving the targeted mineral behind. I think that plenums and DSBs supplement the process that is already occuring inside of proper live rock i.e. rock collected from the ocean. I don't think that plenums/DSBs are obsolete I think people have never really understood the role they play and how to best take advantage of them. It is funny because it is like skimmers people think that the Berlin method is the skimmer. It is isn't it is just one piece of the Berlin.


This is a legit point but from practical experience I haven't see this to be true.

When I start up a plenum, I will squirt frozen food into the first few inches of the gravel (I am trying to get it in the anaerobic area). This seems to make them speed up. Most sumps surface skim and this seems to dump a lot of stuff, but also over time the top of the plenum becomes a biome of it's own. Creatures grow and die there and they all go back to the dust (sand).

Even if this is a consideration, I find the problems of impaired diffusion are far outweighed by having nothing on top of the plenums. Perhaps there could be a way to have one in the DT so that it is bare on top, without being too ugly. Maybe an experiment for another day.


An underrated way of clearing sand beds is to stir them up regularly. I use my hand to do this regularly (maybe monthly or every two months). It is crazy how the water will get all cloudy for a few hours but the next day the tank is brilliantly clear. I also do this hand waving thing to flush the live rock too. I don't think sand plays a super big role in the bed if it is kept under the depth needed for anaerobic decomposition. I am confused by bare bottom tanks, for asthetic reasons but people do what they think is necessary to get their tanks to work.

I love this explanation and it did clear a few things up. My question is: What specifically in a plenum? A DSB is just a 6" or so layer of sand. From my understanding, a plenum is just the area under the sand (which I have no idea how possible that is- i guess your nylon layer is a good idea, but I think i need a visual for what a plenum is). Would water flowing from underneath the sand destroy any possible anaerobic zone? That way there's a constant flow of water supplying oxygen- correct me if I'm wrong. Could I just use play sand (is it fine enough?) for that middle layer? I have this aragonite sand (link) that I could use on top, then the play sand could be deeper?

I do stir my sand bed from time to time, and I siphon it every time I do a water change, but I can't help but feeling like there's a ton of detritus mixed into the sand that I can't get out without a more thorough cleaning.

Perhaps a hanging rockscape (hanging from the back of the aquarium) could keep the rockscape clear. Another possibility is that haveing chaeto or some other type of algae tank would get around the issue, but that's not always the most attractive tank.

 

[duberii]

Another question I have is: is it true that the amount of life that is in the DSB will make it so that there is more planktonic life in the water, which can increase the survival rate of filter feeding life? An article I read said that goniopora do better in these tanks for that reason, but in your experience, do you believe there is more planktonic life?

 

[HuduVudu]

My question is: What specifically in a plenum?

This has rock work on top of it and I don't do that anymore but the set up is the same.

Yes the plenum is the dead area underneath.

Would water flowing from underneath the sand destroy any possible anaerobic zone?

Yes you don't want that.

Could I just use play sand (is it fine enough?) for that middle layer?

You can do this if you are looking for a DSB. You don't really need to do layers if you are doing a DSB.

I do stir my sand bed from time to time, and I siphon it every time I do a water change, but I can't help but feeling like there's a ton of detritus mixed into the sand that I can't get out without a more thorough cleaning.

If you do a DSB or a plenum you must not disturb the lower portion of the bed. You will oxygenate it by gravel vaccing it or disturbing it. This impairs the bed.

Perhaps a hanging rockscape (hanging from the back of the aquarium) could keep the rockscape clear.

This could work. I found the 4" pipe that I used in my 20 to work well and it was easily hidden. You don't need to do the entire bottom of the tank with a DSB or plenum for them to work.

 

[blasterman]

I ran DSBs for years. I found them very stable but didn't buy into the reduced nitrate bit.

What problem are we trying to solve? If the goal is to reduce nitrate a skimmer, or cheato or turf scrubber can be tuned to the level of filtration desired. With a DSB you are limited in terms to what it does. My current fastest growing tank was way too low on nutrients even without a skimmer and heavy feeding. I cut my fuge light cycle in half and my nitrates are where I want them.

As for mechanical filtration, I'm a minimalist, but when I clean my glass or take a toothbrush to the corners of my tank that gunk isn't of much nutritional values to coral. Unless removed mechanically it just decays and pollutes the water column. If your lucky enough to have a tank that never has anything that builds up on the glass you are pretty lucky.

 

[HuduVudu]

Another question I have is: is it true that the amount of life that is in the DSB will make it so that there is more planktonic life in the water, which can increase the survival rate of filter feeding life? An article I read said that goniopora do better in these tanks for that reason, but in your experience, do you believe there is more planktonic life?

These systems are one way to accomplish this, though they don't do it directly. They consume nitrate which helps you to feed more. Which is neccessary for phyto dosing. They help with carbonate buffering which is really helps with invertes especially the low level ones. The also provide low level nutrients to the tank for the filter feeders. So yes there is more planktonic life but it comes indirectly from the plenums/DSBs.

 

[duberii]

This could work. I found the 4" pipe that I used in my 20 to work well and it was easily hidden. You don't need to do the entire bottom of the tank with a DSB or plenum for them to work.

If my ultimate goal is biodiversity/breeding amphipods/nitrate reduction, wouldn't a larger area of DSB be better? I'm sure the effect is scalable, but for most purposes, I'd want the full extent of the benefits, no? In the case of your tank, what was the goal of your plenum?

These systems are one way to accomplish this, though they don't do it directly. They consume nitrate which helps you to feed more. Which is neccessary for phyto dosing. They help with carbonate buffering which is really helps with invertes especially the low level ones. The also provide low level nutrients to the tank for the filter feeders. So yes there is more planktonic life but it comes indirectly from the plenums/DSBs.

I also really don't understand at all how phyto can't really reproduce in our tank (I know it CAN, but it clearly can't reproduce fast enough to make a living culture in our tanks). With all the high power lights we have and such, it seems like phyto should be reproducing and removing nutrients instead of adding nutrients, but i digress....

 

[duberii]

I ran DSBs for years. I found them very stable but didn't buy into the reduced nitrate bit.

What problem are we trying to solve? If the goal is to reduce nitrate a skimmer, or cheato or turf scrubber can be tuned to the level of filtration desired. With a DSB you are limited in terms to what it does. My current fastest growing tank was way too low on nutrients even without a skimmer and heavy feeding. I cut my fuge light cycle in half and my nitrates are where I want them.

As for mechanical filtration, I'm a minimalist, but when I clean my glass or take a toothbrush to the corners of my tank that gunk isn't of much nutritional values to coral. Unless removed mechanically it just decays and pollutes the water column. If your lucky enough to have a tank that never has anything that builds up on the glass you are pretty lucky.

I have multiple goals- biodiversity, stability, and I'd also like more nutrient rich water- not nitrates and such, but proteins, planktonic life to feed corals, etc. The third goal is what I heard a DSB can do- though it seems that was a bit of an oversell. Perhaps, this will come in the form of me dosing phyto, but I'd like a decent microfauna population in the water column that can feed my corals- perhaps an ambitious goal.

 

[HuduVudu]

If my ultimate goal is biodiversity/breeding amphipods/nitrate reduction, wouldn't a larger area of DSB be better?

You have fallen into the man principle.

At night the back of my tank is crawling with amphipods. It isn't the size of the wand it is the magic in it. I think that the plenum/DSB helps with is balance and that doesn't mean it needs to be bigger for that to happen. The constant addition IMO is the key.