Okay, here are some challenges I see to the whole sandbed discussion. Chris,
I would recommend that you do a lot of reading on sandbeds and educate
yourself on them before you decide what you want to do. You will find there
are hundreds of ways to set them up, and different opinions among everyone,
even those who advocate the use of a deep sandbed.
Here is how a deep sandbed is supposed to work. In a sandbed of 4-6 inches
of depth (or deeper for that matter) there are 3 zones of microbial bacteria
that help convert the protiens in your water into ammonia, nitrite then
nitrate and in properly working sanbeds, into a nitrogen gas which is
harmless to the system and escapes in the form of a bubble into the
atmosphere surrounding the tank.
Zone 1, which is found on the top of the sand bed is the Areobic Zone. These
are bacteria which rely on heavy amounts of oxygen in the water to survive.
They are not very efficient at converting waste into nitrates, and do not
convert nitrates into gas, thus with only these bacteria, tanks tend to
build up a high amount of nitrates. That is why wet and dry filtration is
not recommended in a reef. Wet and dry filtration relies heavily on aerobic
bacteria, and they rapidly convert waste into nitrates which then remain in
the system until removed through water changes.
Zone 2 is Anoxic Bacteria. These bacteria are the most efficient of the 3.
They are found starting about 1 inch under the sand and go down an inch or
two into the substrate. They survive with a small amount of oxygen, although
they must have some to survive. They are capable of converting the waste all
the way down into nitrogen that then is released into the system, which
floats to the top and pops, releasing it into the atmosphere. These bubbles
are the bubbles that many aqaurists question when they set up a deep sand
bed. They are often not sure what they are. These bacteria are the ones in
Live Rock that help our system so much. That is why LR became the backbone
to succeful systems. These bacterias are found about .25 inches under the
first layer of LR.
Zone 3 is Aneorobic Bacteria. These bacteria are the least efficient of the
3. They are the bacteria that survive with no oxygen. They are responsible
for converting waste into hydrgen sulfide, which can, in large amounts, wipe
a tank out rather quickly. They are found at 2-3 inches down in the sand,
and can grow as far down as the sand is deep. These are the ones that strike
fear into the hearts of aquarists.
The goal in a deep sand bed is to have enough Anoxic bacteria to support the
system by converting all the waste it produces into nitrogen. Most deep sand
beds do also have aneorobic bacteria, but because you are not supposed to
disturb a deep sandbed, these bacteria and the hydrogen sulfide they produce
is not introduced into the system in amounts large enough to have and
adverse effect on the tank.
IMO, one of the biggest problems with sandbeds, and measuring the
effectivness of sandbeds within the hobby, is that too many people set them
up too many ways. Most people dont realize that you should not mix sand
stirring fish into a tank with a deep sand bed, or that it is recommended
that tanks with deep sandbeds have large amounts of caluerpa or xenia in the
system to help remove excess nutrients.
Ron Shimeck, and many others who support deep sand beds in their tanks
recommend sandbeds of at least 3 inches. Most even say 5-6 inches is best.
They recommend you start the sandbed with as much live sand as possible, but
recommend that you begin with at least 50% LS and 50% small aragonite
substrate. Once the sandbed is in place, Ron recommends that you add a "live
sand kit" which is animals of different faunas that will help populate the
sandbed. He also recommends that you have a refugium in the system to grow
caluerpa or xenia in. These are used as export mechanisms in the system to
help "export" excess nutrients that the sandbeds cant handle. Ron Shimeck
himself uses large amounts of caluerpa in his system, and last I heard, was
exirmenting with xenia. You also dont want to use sand stirring fish in your
tank if it has a deep substrate. They will disturbe the differnt zones I
wrote about above, and thus kill the anoxic bateria that are trying to
reproduce in the sand. They can also dig deep enough to release hydrogen
sulfide pockets. Same is true for gravel vaccing the sandbed. Dont do it. It
is not the correct way to manage your deep sandbed. Ron recommends sea
cucumbers and Nasarius snails to help move the substrate. They do it slowly,
and do not move enough sand to destroy baterial populations. Tanks with deep
sandbeds can not be overpopulated with fish, and you must be careful not to
overfeed.
Personaly, I wouldnt put a deep sandbed in my tank. I know people who have
them and love them. But I also know more people who had them that have had
terrible luck with them. It was not the aquarists fault. Somwhere along the
line, they are given bad advice and one thing leads to another and the tank
crashes. IMO, deep sandbeds are ticking timebombs (for most ppl). The
sandbeds do a great job for a while, but sooner or later, the waste that is
produced in the tank can not be processed quickly enough by the bacteria in
the sandbed. As time goes on, the wastes build up and build up, and then
algae begins to grow. Then it grows out of control. Sooner or later, the
system simply ovewhelms itself, and crashes. Many times this will lead to
the death of corals.
I use, and would recommend a thin sand bed. I use about a 1 inch sandbed,
that is in the tank purely for looks. I rely on my live rock for my
bacterial filtration, and I use a skimmer as well. I am the export mechanism
for my tank. I do my water changes weekly, and when I do them, I gravel vac
as much detrtitus from the tank as I can. If the detritus is not in the
tank, it does not have the chance to become protiens, ammonias, nitrites and
nitrates. My tank has been running for almost 2 years now, and I register a
big zero on my nitrate test kit. I feed daily, and have 9 fish in a 70
gallon system.
Thats it. IMO, deep sandbeds are a risk. If you are going to do it, send Ron
S. an email and let him know you want to put one in your tank and ask him
specifially how he would recommend you do it. He will probably lead you to a
website or list serve that has his exact instructions. At least that way you
know you followed an "experts" instructions.
Sorry everyone for the long email, and for any spelling errors, I didnt
spell check it!
Shane C.
> -----Original Message-----
> From: Marco Delsordo [SMTP:[EMAIL PROTECTED]]
> Sent: Tuesday, August 28, 2001 12:17 PM
> To: [EMAIL PROTECTED]
> Subject: RE: substrate depth ?
>
> It�s recommended to have a 2" or 3" deep susbtrate, because if it is too
> deep, dead spaces will form causing lots of hydrogen sulfide.
> I have a 2" sand substrate and it works great because when i move it, lots
> of nitrogen bubbles go up to the surface, which proves that anaerobic
> bacteria are doing their job.
> Also a fine sand substrate will not clogg by detritus, because the sand is
> so fine that it can�t penetrate into it, it will just stay over the sand
> until it desintegrates and the filter and skimmer takes care of it.
>
> -----Original Message-----
> From: Neptune [mailto:[EMAIL PROTECTED]]
> Sent: Martes, 28 de Agosto de 2001 02:04 p.m.
> To: [EMAIL PROTECTED]
> Subject: Re: substrate depth ?
>
>
> I have also heard about the dangers of making the sand bed too deep which
> can lead to "dead" spots. These can release sulfur dioxide into the water
> killing most of the tank. It's very important to have lots of sand
> stirring
> organisms to keep the bed well mixed. FWIW
>
> Craig
>
> > Can you guys explain to Chris why the deeper the substrate the better?
> And
> > why 50% crushed coral is better than a mix of LS and dry aragonite
> > substrate? IMO, it is important for people asking these types to know
> some
> > details, specifically what you consider the benefits of the deep sand
> beds
> > to be, how they work and why.
> >
> > Shane
>
> ________________________________________
>
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