Sand turning to rock

[Gravesj1s]

Good analogy!
It does seam the amount of quantified information is surpassed by the amout of here-say.

Something just seams, alittle ....mmmmm:idea: peculiar when your tank starts to look and operate more like an "antfarm" than a reef.

 

[tmz]

Don't get me wrong ,
I like 4+ inch sand beds and the animals they support including the micro fuana and worms, wrasses, jawfish, certain anemones, etc., but there are other options for denitrification.

Once it was clear to me that denitrification occurred in very shallow sediment or even bacterial mulm, deep beds and some of the hypothesized but unproven dos and don'ts and endless often acrimonious debate became less interesting .

In my opinion , the biggest misconceptions center on the dynamics in a deep bed and a lack of focus on the needs of the facultative heterotrophic denitrifying bacteria which the bed is supposed to support in a denitrifying application. A deep bed of sand can't support these bacteria in anaerobic denitrification unless there is enough water movement in the deeper areas to insure a hypoxic environment(low O2 with NO3) without going to an anoxic enivronment(no O2 and no NO3). The latter sets the stage for sulfate reducing bacteria and their byproduct , hydrogen sulfide when tidbits of organic carbon are present such as that in the heterotrophs that die in anoxic water which they themselves can create by exhausting the oxygen and NO3 if it's not replenished in their locale.

There also has to be a way for organic carbon to move into the bed since the heterotrophs need it along with a little phosphate and nitrogen. So it's a pretty delicate balance between the amounts the bacteria consume and the amounts provided which for the most part relies on benthic fuana to keep channels open and move some nutrients around.

While some diffusion, molecular equilibration , will occur in water , it's a pretty weak force in the bed and won't add much to the deeper areas of a sand bed. Advection ,upwelling caused when horizontal current encounters obstacles like rock work and causes a subsequent downward flow , is a bit better but still not strong enough to penetrate very deeply in much volume. Thus, it seems there is a need for a healthy live bed with organisms to keep it channeled and move some nutrients down.Keeping such a live bed will likely require periodic replensihment/replacement with live sand and enough food or animal waste to support the sand critters.

Then on top of all that clumping can occur from on /off bacterial activity and localized ph changes in the bed. Localized anoxic conditions and associated ph changes may also unbind some metals from refractory organics in an older bed .
There are many reports of deep sand bed failures from seasoned aquarists. Apparently, they can become clogged and ineffective or harmful without some efforts at methods to keep them healthy.

Unfortunately, there are a lot of anecdotes and opinions about methods but little in terms of actual practices and long term successes.There are a dearth of documented accounts of long term (beyond 5 years)effective sand beds, at least that I have been able to find, and no protocols for keeping them effective much longer other than vagueries about replenishment and benthic fuana,flow, depth ,grain size , optimal and banned cleanup crew members, etc.
I ran a deep sand bed for over 7 years; did some replenishment over the years ;probably could have done more, and; then siphoned most of it out after nitrates took off.
FWIW at this point I keep mostly shallow beds with some deeper pools of sand for wrasses and my pistol shrimp.I'll probably try another deep bed at some point since they are aesthetically pleasing to me and I enjoy the thought of all the activity in them.

 

[pascal32]

Don't get me wrong ,
I like 4+ inch sand beds and the animals they support including the micro fuana and worms, wrasses, jawfish, certain anemones, etc., but there are other options for denitrification.

Once it was clear to me that denitrification occurred in very shallow sediment or even bacterial mulm, deep beds and some of the hypothesized but unproven dos and don'ts and endless often acrimonious debate became less interesting .

In my opinion , the biggest misconceptions center on the dynamics in a deep bed and a lack of focus on the needs of the facultative heterotrophic denitrifying bacteria which the bed is supposed to support in a denitrifying application. A deep bed of sand can't support these bacteria in anaerobic denitrification unless there is enough water movement in the deeper areas to insure a hypoxic environment(low O2 with NO3) without going to an anoxic enivronment(no O2 and no NO3). The latter sets the stage for sulfate reducing bacteria and their byproduct , hydrogen sulfide when tidbits of organic carbon are present such as that in the heterotrophs that die in anoxic water which they themselves can create by exhausting the oxygen and NO3 if it's not replenished in their locale.

There also has to be a way for organic carbon to move into the bed since the heterotrophs need it along with a little phosphate and nitrogen. So it's a pretty delicate balance between the amounts the bacteria consume and the amounts provided which for the most part relies on benthic fuana to keep channels open and move some nutrients around.

While some diffusion, molecular equilibration , will occur in water , it's a pretty weak force in the bed and won't add much to the deeper areas of a sand bed. Advection ,upwelling caused when horizontal current encounters obstacles like rock work and causes a subsequent downward flow , is a bit better but still not strong enough to penetrate very deeply in much volume. Thus, it seems there is a need for a healthy live bed with organisms to keep it channeled and move some nutrients down.Keeping such a live bed will likely require periodic replensihment/replacement with live sand and enough food or animal waste to support the sand critters.

Then on top of all that clumping can occur from on /off bacterial activity and localized ph changes in the bed. Localized anoxic conditions and associated ph changes may also unbind some metals from refractory organics in an older bed .
There are many reports of deep sand bed failures from seasoned aquarists. Apparently, they can become clogged and ineffective or harmful without some efforts at methods to keep them healthy.

Unfortunately, there are a lot of anecdotes and opinions about methods but little in terms of actual practices and long term successes.There are a dearth of documented accounts of long term (beyond 5 years)effective sand beds, at least that I have been able to find, and no protocols for keeping them effective much longer other than vagueries about replenishment and benthic fuana,flow, depth ,grain size , optimal and banned cleanup crew members, etc.
I ran a deep sand bed for over 7 years; did some replenishment over the years ;probably could have done more, and; then siphoned most of it out after nitrates took off.
FWIW at this point I keep mostly shallow beds with some deeper pools of sand for wrasses and my pistol shrimp.I'll probably try another deep bed at some point since they are aesthetically pleasing to me and I enjoy the thought of all the activity in them.

you know too much

 

[Gravesj1s]

~tmz,
I like the diversity a sandbed can add as well as understand certain species benefit and may actually require a DSB.Like you,I've also,done the DSB setup both with & w/o the plenum.It ran for about 5 years or so before breaking the tank down in 98' and leaving the hobby until 08-09.
About a year prior to dismantling is when I started to realize how little evidence there actually was to backup the claims of the DSB but,knowing I was leaving the hobby I let it be.
I respect your veiw and appreciation for the things a DSB can add,but beyond that I think I have a different veiw.

As far as the substrate clumping issues go I noticed when I dismantled my dsb about an inch under the surface it had large chunks throughout that were solidified.

I do have some questions about some things that pertain to your last post I hope you dont mind continueing this discussion or anyone else that might be interested in discussing some of the things that are relevant to the thread.

 

[tmz]

Hi Graves. Don't see where we have differing views based on the posts. I like probative discussion,particularly when it comes to sand beds since there isn't much hard evidence or firm discussion on methods but there is a good deal of fanciful verve out there.

 

[Gravesj1s]

tmz,hi. sorry for the delay, must have been a misconception on my part.

FWIW-Got myself dragged into a debate regarding DSB,something I didnt want anything to do with.Dont know why they just didnt post here.
Sorta burnout now on the topic,at the moment anyway.I'd would still be interested at another time ,discussing things that are important to dsb & ssb what size ,type sediments might be best for certain marine life ect....It is a vague area ,atleast to me.
Look forward to it if and when it comes up.

 

[tmz]

Right , I get pulled into those from time to time and they get as nasty as a 10year old plenum.Feel free to ask or debate anytime. I promise not to throw sand around .

 

[reefplicate]

this is what happen to my 10yrs old tank running on plenum system which i tore down due to leakage of the silicon.

its a real pain in the bud trying to remove concrete from the tank...
sand remained clean with only a few small areas with H2S which was where live rocks set...

my new tank will be just 2" depth mixed sand between 2mm-5mm

cheers