Grey patches patch under sandbed

[koniyakutz]

Hi guys,

My tank is abt 6wks old and I have noticed several dark grey patches under my sandbed, one of the patches is quite large and it seems to be 'growing'.

Is this normal?

I was told not to disturb the sandbed as it might release toxins and crash the whole tank.

[madmac]

Its probably H2S... sometimes blackish looking...

so the quick way is to make sure that the area above gets lots of flow. Do it in such a way that it does not stir up the SB... tis won't solve the problems that will come and the SB where H2S resides is dead...,no bacteria, no critters will go near there, to make barrows, find food, etc... and it will "spread".

I went thru' a conversion to BB due to discovering some patches of these, documented in my tank thread, best to you.

[Kelmen]

Eh, so those patches are bad stuff? I though they are the "natural" process in DSB!

I got them in my refugium mud type sand bed, probably flow not good enough.

I got DSB in main tank too, but with 0 grade sand, no such patches.

[koniyakutz]

A pic of the patch ...

[blueheaven]

Definately hydrogen sulphide

Its a poisonous substance but usually it would not accumulate to fatal concentrations in our tanks. Just get you sandbed oxygen rich water and it'll go away

[decentkid]

previously i asked this in RC, and Dr Ron (if i never remember wrongly) replied that this is a kind of cyano, not hydrogen sulphide, reason: cos hydrogen sulphide is colourless

anyone has any idea?

[Gouldian]

previously i asked this in RC, and Dr Ron (if i never remember wrongly) replied that this is a kind of cyano, not hydrogen sulphide, reason: cos hydrogen sulphide is colourless

anyone has any idea?

I second Decent kid on this.

In "Reef Invertebrates" by A. Calfo and R. Fenner, it is written: "Contrary to popular misconception, the discoloration of sand visible substratum through the glass is not dangerous anaerobic activity or even indicative of other organisims spread throughout the rest of the sand bed. The 'colours' most often are simply algae and other micro-organisms flourishing in a very thin layer bewteen the glass and sand from direct and refracted light through the aquarium. (H. Schultz)."

[blueheaven]

Cool...will look up on that

[madmac]

oh dear... ... koniyakutz, take a straw, dip it into the sandbed, right down to the black sand and carefully remove a sample... you should start to smell something... something bad, like a drain thats not been opened for some time... don't put it too close to your nose....

its black because its dead, nothing is alive there(do you notice anything alive around the area? A thriving SB is one which supports all sorts of life esp pods & worms)... theres definitely no cyano, there... if you hv cyano there, you'll hv cyano on the surfaces first...

Dr. Ron is the guy who coined DSBs... you can't talk about DSBs without mentioning him...he is father of DSBs... and A. Calfo and Bob Fennel makes a living by books on DSBs and others

your pic show the SB surface is covered by algae.. which is preventing the O2 exchange needed to remove H2S, syphon out the top layer of sand first before you do anything else... Its actually quite rare to see pics where the black layer is up the front glass... usually there is a layer of algae there, which will give out O2, and pushes the H2S back in, in most cases its hidden... a late discovery is often times unfortunate..

jus my opinion, pls don't take tis personal.

[Gouldian]

No worries, we are all learning here. You may be right Madmac.

[koniyakutz]

Oh no .....

My tank is only 6wks old and its still cycling, will do the smell test tml.

I can see several small "tunnels" in the SB and lots of tiny white creatures(are these pods?) on the glass surface and near the SB.

Will remove the top layer of sand and add a M620 this weekend for more water circulation.

I may have compacted the SB as the sand was from another tank and I poured it in while it was wet.

[koniyakutz]

Did I made a mistake by using natural fine sand for the main tank? Seems that its more commonly used for DSB in sumps.

[madmac]

could be both, the poison sand from the contaminated tank and fine sand which restricts water flow/movement into the SB...

imo, thats a very large area to do nothing about it.

[koniyakutz]

for the help guys, really appreciate it.

I did the smell test this morning, OMG .... it stinks to high heavens !!!

Smells like swamp + choked drain + super bad breathe .....

I plan to do the following this weekend,

1) Suck out the surface sand to get rid of the diatoms and dirt

2) Add a M620 for additional water circulation

3) Try to looson the SB by using a toothpick to poke poke.

The patch will go away once it gets enough waterflow?

[koniyakutz]

Taken from http://aqualinkwebforum.com/eve/ubb.x/a/tp...22/m/6626071522

Decomposition of organic detritus is a very complex subject, and I cannot possibly do justice to it here. Even though I discuss it in the FAMA sandbed articles, in fact I only devote about a page to it there, and say right up front that I'm only scratching the surface. I'll just try to give you a basic overview of the processes here (and feel free to jump in and correct me DBW if I'm butchering the chemistry ).

Decomposition can be either aerobic (taking place in an oxidizing environment) or anaerobic (taking place in a reducing environment). You're probably thinking, "Oh, no -- here comes that redox potential stuff again," but what exactly is all this "redox potential" stuff about? Well, technically, redox potential is a measure of the energy gained in transferring 1 mole of electrons to an oxidant (such as oxygen, nitrate, sulfate or methane) from hydrogen gas. Unless you're a chemistry buff (unlike me) that probably doesn't help you much, does it? Well, in order for any organism to survive it needs energy, right? We get energy by "burning" (oxidizing) ATP (remember that "powerhouse of the cell" class in high school biology?). That means that we break down sugars, using oxygen (O2) as our electron receptor, and release carbon dioxide (CO2) as a waste product of that redox (reduction/oxidation) reaction. We use the energy of transferring an electron to fuel our bodies, but because there are really no free electrons running around in the environment, for every reduction there is a corresponding oxidation (hence the term redox). Well, respiratory processes of living organisms are essentially oxidation-reduction (redox) reactions involving a variety of oxidizing agents (electron receptors). These redox reactions occur by the transfer of an electron from one material to another to harvest energy, and much of the energy flow in marine sediments is regulated by the availability of suitable electron receptors

We generally think of oxygen as the primary requirement of life, but oxygen is not always the electron receptor of choice -- depending on the environment and the concentration of available electron receptors (this is measured by redox potential in a manner analogous to measuring the availability of protons with pH), other compounds are the most efficient electron receptor for that energy transfer. There is a highly predictable gradient of biochemical pathways as you go deeper into marine sediments. Oxygen is obviously the most important and common electron acceptor for most organisms that we want in our tanks (everything we can see), but in marine sediments O2 is rapidly depleted, and other electron receptors, such as nitrate, sulfate, carbonate and methane become the primary avenues of energy transfer. Anaerobic reduction, primarily by facultative anaerobes which preferentially use NO3 as the electron receptor in the presence of low oxygen concentrations, is obviously the most desirable of the redox reactions occurring within the sediments, in terms of maintaining a low nutrient environment within a closed aquarium system, but the other biochemical pathways are important as well.

Because of the name given to the biochemical pathways, people often have the misconception that deep sediments somehow produce a bunch of sulfate that has to go somewhere, but in fact sulfate is common in seawater, the deeper sediments can actually use these "wastes" as their source of energy, too. It is only in an unbalanced aquarium that problems of excess hydrogen sulfide occur. As Doug pointed out, the stuff that diffuses upwards into the aerobic portion of the sandbed is rapidly oxidized and diffusion is too slow to cause toxicity problems (it is only the fabled black smoker volcano-eruptions" that release enough H2S to really cause concern, and this should never happen in a properly maintained tank, regardless of the design). The bottom line is that no matter the tank design you use, the amount of nutrients added to the system must be equal to or less than the amount exported (through filtration, skimming, uptake and aquarist intervention) or the tank will fail -- no two ways about it. Whether you use a sandbed or not, if the nutrient load in the tank exceeds the capacity of the "filtration" (I use this term in the loosest possible sense of the word) then the tank is simply bound to fail. Having a sandbed is *not a magic bullet* that allows you to cast all concerns about nutrient cycling to the wind, it is simply another method of providing "filtration" for the tank, and happens to be the way in which natural reef systems are "filtered" by the adjacent mangrove, seagrass and estuarine habitats.

The basic idea is this: at the water-sediment interface, oxygen is readily available, and aerobic respiration dominates the respiratory pathways. Depending on the organic load and grain of the sediments, oxygen can be very rapidly depleted. In most fine sediments, such as I have recommended here and elsewhere, oxygen is depleted within the first 0-4cm. As available oxygen decreases, nitrate (NO3) reduction becomes the most favorable respiratory pathway. This layer is generally very thin (usually on the order of 1-2 cm or less), and as the NO3 is reduced, sulfate (SO4) and carbonate (mostly CO2) reduction becomes the dominant metabolic pathway over the next 10-50 cm. Below this (if you plan to add more than 50 cm of fine sand to your aquarium for your sandbed methanogenesis dominates.

In most natural marine sediments in the habitats associated with reefs, the depth at which sulfate and carbonate reduction begins to occur is about 10cm, so by using sand of approximately the particle size and composition of natural sediments in estuaries, mangroves and seagrass beds, an aquarium sandbed on the order of about 10 cm deep *should* accomplish the goal of optimal nutrient recycling within the aquarium (although there are MANY factors that can dramatically affect this number and it is impossible to say if it will happen in a tank by dumping in 10 cm of fine sands -- the only way to know is to try and watch for the sulfate reduction zones). This paragraph is basically the start of the discussion Richard Harker and I had on this subject a while ago, which Doug has archived on his web page.

OK, with that background, I'll try to finally answer your question. As I mentioned above, anaerobic respiration is most limited by appropriate electron receptors. As we load our systems, we continually add detritus (a carbon source), but our anaerobic bacteria are limited by electron receptors such nitrate and sulfate, not carbon, and the detritus starts to pile up. At the same time, the aerobic pathways continue to chug along, churning out NO3. Because the aerobic bacteria are carbon limited, the increased organic load allows them to increase both their population sizes and their rate of processing these organics. This speedup in aerobic metabolism means that oxygen begins to be used more quickly in the sediments, and the penetration of oxygen into the sediments is reduced. Reduced oxygen in the sediments leads to increased zones of anoxia, and the anaerobic reduction pathways start to roll. These can be remarkably efficient (more so than the aerobic pathways) when electron receptors such as nitrate and sulfate are readily available, and soon you notice the spread of the sulfate reduction zones in your sediments. If all is well in your tank, this condition should lead to organics being broken down faster than they are introduced into the system (at least, this is ideally the goal of any closed system such as an aquarium -- again, if such a balance between inputs and exports cannot be reached, the system will crash regardless of its design), and as those nutrients are recycled, the anaerobic zones begin to become limited by the availability of electron receptors again. Sulfate reduction zones ebb, and the cycle starts again.

The "pseudoequilibrium" between nutrient input and recycling of nutrients by the sandbed *should * allow the system to run with minimal export mechanisms and modest regular water changes (again I emphasize should, because there are a LOT of factors that differ from tank to tank and which have a *major* impact on how deep and/or effective the nutrient cycling will be again, the only way to really be sure is to do it by a little trial and error) . This natural cycling of nutrients mimics the ebb and flow of nutrients on natural reefs and their associated sandy habitats, and IMO is a much more simplistic and elegant method of aquarium design than the extreme chemical micro-management of reef aquaria that has become increasingly popular over time.

Clear as mud now?

Rob

[madmac]

I plan to do the following this weekend,

1) Suck out the surface sand to get rid of the diatoms and dirt

2) Add a M620 for additional water circulation

3) Try to looson the SB by using a toothpick to poke poke.

The patch will go away once it gets enough waterflow?

I don't know... you don't seem overly worried over H2S in your tank, to care about why/how it gets produce and spread... you rsch articles on DSBs instead ...! There are some of us who would lose sleep knowing that there even a small patch existing. K, in the first reply, we didn't get to see the extend of your situation... but when the pic came out, you could now smell it...

Here's a small hint on what to do... Get rid of your sand!... what are you thinking...!

I'm sorry, I just can't help it.

[decentkid]

bro...just my 2 cents, but DSB can become a time bomb due to a build up of organic materials and H2S over time....best if u can maintain the number of critters in the sand bed with will continously shift the sand bed, will allow the bacteria to work better and also release small amounts of H2S over time

madmac: i have to agree with what u said, however, i also wish to know why is the black patch H2S when H2S is colourless???

[blueheaven]

bro...just my 2 cents, but DSB can become a time bomb due to a build up of organic materials and H2S over time....best if u can maintain the number of critters in the sand bed with will continously shift the sand bed, will allow the bacteria to work better and also release small amounts of H2S over time

madmac: i have to agree with what u said, however, i also wish to know why is the black patch H2S when H2S is colourless???

That's a common problem amongst reefers. Most of them think that they can set up a sandbed by just adding the sand and it just stops there. That's why I came up with the article to provide a simple but detailed explaination of sandbed dynamics which i wish reefers who are setting up a sandbed read first before setting it up.

Actually, a properly set up and maintained sandbed can provide maximum chemical filtration and can even change to provide maximum effeciency should the tank water conditions change. You just imagine, most bacteria can reproduce (binary fission) every 20 mins under the right conditions, you almost have a frontline of soldiers standing by to help if anything bad should come.

[madmac]

You just imagine, most bacteria can reproduce (binary fission) every 20 mins under the right conditions, you almost have a frontline of soldiers standing by to help if anything bad should come.

Then what happens... you get an over-crowded SB, filled with either bacteria/critters growing in mass and numbers... they push each other out(sink is full), require more resources(as in O2, nutrients) or they will die (and cause a chain reaction)...think about it... time-bomb or bomb going off after some time, same meaning.

SB do what they are meant to do... no different from what they do in nature, hv you been to Chek Jawa? do you see acros/LPS there... do you find sea-cumcumbers, softies there?

Besides its either DSBs or BB, nothing in btw... 3.5" is not anaerobic enough... you only get the bacteria doing the A to NO2 conversion....?

dk, no bacteria, critters, worms, algae can live thru'/around/shift H2S areas... nothing is alive, it is more than dead... it is not even decomposing... and if thats not bad, how about it being toxic, worse? are you referring to the chemical properties of H2S, in it being colourless, is not he colour by what they do....hv you seen the colour of an Egyptian mummy unwrapped? I don't know where I've read this, but one tank had a crash when H2S burped out of the SB... maybe the owner thought that it was nitrogen bubbles, and his tank going thru denitrification... but the smell, the smell... ; )

Actually, its not as toxic as believed, most mushrooms, carpet anemones, and sea-cucumbers/fish/and pistols are probably quite H2S resistant... I have a pair, they do wonders to area under the LRs as they find shelter and was constantly seen making tunnels, shifting sand in hurry... about the only place they don't do is in front where the fish swim about... and guess what, thats the very area where I discovered my H2S patch... once a H2S patch starts to form its gets only larger, O2 rich water seeks to keep in, but it will spread(that pic above is a good eg of how it goes), it keeps others animals away.

BTW, H2S is the resultant chemical by-product of a complex-chain of reactions coming from the anoxic bacteria region of the SB, as P is process and pass-on... pls, don't ask me to prove it... bc I can't.... its somewhere in RC

[blueheaven]

What we want is not an anaerobic region. We want an anoxic region which still consists of minor traces of oxygen. As for bacteria overcrowding, I have stated in my article under "Quorum Gene Sensing" that bacteria are able to control their population by quorum sensing.

And to the bane of Singapore reefers, most of us do not even have enough infauna in our sandbeds, not say overcrowding. Even I had to resort to culturing my own infauna to replenish my DSB.

And lastly, the depth of a sandbed, as mentioned in my article, depends on the water that is passed through them.

And from what I learnt, H2S is produced when sulphide salts (probably from sulphur containing organic compounds) are decomposed and dissociated to ions, one of which is sulphide ion. The sulphide ion then reacts with the hydrogen ions in water to form H2S and this process is decreased with increasing pH. Furthermore, the amount of undissociated H2S decreases as salinity increases in a constant temperature and pH.

Then in this case, why do we have H2S forming in our tanks?

[decentkid]

yes...the both of you are correct, H2S are formed from decomposition...if the SB detritivours are of appropriate amounts, the amount of H2S produced is reduced...but however, if a pool of H2S does get accumulated, then that area can be a death zone, thats why the need for critters to prevent that from happening

on the other hand, H2S will dissociate in the water to become a weak acid and will react with oxygen to form sulphuric acid, but marine environment is usually an alkaline one...and also a weak alkali...so the reaction rate is slow...if less oxygen does reach these regions, the weak acid cannot become sulphuric acid and cannot react completely so the tendency to accumulate till horrible levels

now what i am trying to find out is...how to conclude that the black regions are hydrogen suphide when hydrogen suphide is colourless??

[madmac]

so the bacteria stops, and the critters? do they know Quorum Gene Sensing too?

anyhow the whole viability of DBS is that one is actually keeping another galaxy of sand animals to support reef-keeping (animals in deep, clear, nutrient free waters..) now in your article, claims are made that theres not enough in-fauna for SB to sustain life... what about NO3, N and P, the basis of all forms of life, isn't there enough there to give everyone problems with just algae alone... and you want to add more...? you lost me there.

[blueheaven]

so the bacteria stops, and the critters? do they know Quorum Gene Sensing too?

anyhow the whole viability of DBS is that one is actually keeping another galaxy of sand animals to support reef-keeping (animals in deep, clear, nutrient free waters..) now in your article, claims are made that theres not enough in-fauna for SB to sustain life... what about NO3, N and P, the basis of all forms of life, isn't there enough there to give everyone problems with just algae alone... and you want to add more...? you lost me there.

Nope, sadly infauna do not posess the quorum gene

Yes, you may have the basis of all forms of life, you may have algae but where do the infauna come from? The LR we purchase for our refugiums are already half dead and you expect to have a thriving community? And also unlike other countries, Singapore lacks "recharge kits" being sold to us. And also, algae is not an infauna, should call it "inflora"

[decentkid]

so the bacteria stops, and the critters? do they know Quorum Gene Sensing too?

anyhow the whole viability of DBS is that one is actually keeping another galaxy of sand animals to support reef-keeping (animals in deep, clear, nutrient free waters..) now in your article, claims are made that theres not enough in-fauna for SB to sustain life... what about NO3, N and P, the basis of all forms of life, isn't there enough there to give everyone problems with just algae alone... and you want to add more...? you lost me there.

bro...those critters do have a food web of their own lar....fishes and other things will consume them....

and yes i agree that a DSB will give one worries...adding to algae problems...but DSB do have their use if maintianed properly

and to add....H2S will kill both denitrificating and nitrificating bacteria....but there is also another aerobic bacteria that will reduce the H2S sulphate....its a whole cycle in the tank...but the tricky apart is to prevent the build up of H2S...and that is when u really have to maintain the sand bed....

[madmac]

thank you both for your explanation... I've come away wiser. inflora/infauna, recharge kits, fishes and other that feed on critters and the food web etc.. : ) no, I'm still thankful... at least you corrected where I was wrong. : )