Pros vs Cons: Deep Sand Bed vs Shallow Sand Bed

ManOfSalt · Feb 25, 2014

vlangel said:
Hi all. I've been following this thread because In the late 1990's I worked at a LFS and my boss was a fan of DSB. I learned of the function of one as a nitrate reducer without really understanding the science. I only knew the importance of not disturbing the anaerobic bacteria at the bottom and keeping a healthy colony of creatures at the surface. My question now is: where do the anaerobic bacteria come from when a DSB is put in? I assuming the creatures on the surface come from seeding a tank with LR but I am at a loss to imagine where the anaerobic colony comes from?

I'm not quite sure on this one but I would assume it's like any bacteria in that If the conditions are suitable in the environment, it'll just grow. Kinda like the bacteria that grows on meat or liquids that are left out too long. In this case suitable conditions are low oxygen. I could be very wrong though =\

Eienna · Feb 26, 2014

Correct, to the best of my knowledge.
They will be present but will not be able to multiply or do their job without the proper conditions. Their transformation of nitrate to nitrogen gas requires low-oxygen conditions.

vlangel · Feb 26, 2014

That is what I thought also but then "experts" will tell you that you never ever can move them, as in from one tank to another. That you will completely destroy it. Maybe what they mean is you destroy it to the point that you might as well start over with just seed sand. That makes sense.

ManOfSalt · Feb 26, 2014

Ya that makes sense to me as well based on info that I've gathered about it. So like say if you have a SSB, anaerobic bacteria probably won't be present but then you increase the depth of your sand to 4" or more, they will begin to grow. Then if you try and move it (which would entail stirring the sand) it goes from a low oxygen environment (hypoxic?) to a higher oxygen environment (oxic?) no matter how you look at it. Then I would imagine it would just die off because it can't function in those conditions. I would also imagine that apart from killing off the anaerobic bacteria you would see a spike in levels. Probably mainly nitrate? I'm not 100% sure though just going off of reading and not experience D:

Eienna · Feb 26, 2014

ManOfSalt said:
Ya that makes sense to me as well based on info that I've gathered about it. So like say if you have a SSB, anaerobic bacteria probably won't be present but then you increase the depth of your sand to 4" or more, they will begin to grow. Then if you try and move it (which would entail stirring the sand) it goes from a low oxygen environment (hypoxic?) to a higher oxygen environment (oxic?) no matter how you look at it. Then I would imagine it would just die off because it can't function in those conditions. I would also imagine that apart from killing off the anaerobic bacteria you would see a spike in levels. Probably mainly nitrate? I'm not 100% sure though just going off of reading and not experience D:

Sounds about right...

vlangel · Feb 26, 2014

My tank has a DSB which is why I wanted to understand it better. Yesterday I bought a nitrate kit and tested it. I should be ashamed I know having this tank up almost a year and a half and never tested for nitrates but what can I say? Anyway they were zero so I'm going to surmise that my DSB is functioning as a denitrifier in spite of the fact that I moved it from my 90g a year ago. It probably went through a period of not functioning well when first moved but now is probably pretty good. At least my test results were good.

ManOfSalt · Feb 26, 2014

Excellent! So you just dug it up and transferred it? Do you remember anything drastic happening around the time that you did it or did you sort of quarantine everything for a while?

Eienna · Feb 26, 2014

It will reestablish if moved, but if you kill off the critters while moving it you could have yourself a lovely little ammonia spike.

vlangel · Feb 26, 2014

ManOfSalt said:
Excellent! So you just dug it up and transferred it? Do you remember anything drastic happening around the time that you did it or did you sort of quarantine everything for a while?

Yes sir, that's what I did. I did plan it out so that the entire transfer was done in about 3 -4 hours. The 90g was in the same spot that I wanted the 36g to go so after the bulk of the tank was drained, ( I left enough SW to keep the sand wet) I scoop the sand into buckets. When the 90g was emptied enough so my husband & I could move it we did. Then I immediately began setting up the 36g. As soon as the sand was in I scaped it and then put probably 20g of SW from the old system in. I mixed the rest fresh as a WC. All my fish and corals were in a 20L which was woefully too small so they went right in the new system as well. I bought an ammonia kit to watch the ammonia closely and it never went above the first color change,(.025 I think ) and in a week and a half was 0. I didn't even bother buying a nitrite or nitrate kit since die off was so insignificant. Considering that I was putting 7 fish in, which is pushing it for a 36g anyhow, I guess I was taking a risk. I didn't lose a single fish or coral though.

vlangel · Feb 26, 2014

Eienna said:
It will reestablish if moved, but if you kill off the critters while moving it you could have yourself a lovely little ammonia spike.

I guess I didn't kill too much off since I was monitoring ammonia and never had much of a spike. I was worried about that and prepared to do a lot of WCs often if necessary. I even added a clam a month or so later and it did fine. Thinking back that was probably foolish but the tank was operating very stable by then.

Mike J. · Feb 26, 2014

I have moved a 55 gal. tank with a 5" DSB two times. I took everything out except the sand and just enough water to keep it wet. Set it back up and never had a loss of any kind. I guess the tank could have leaked or something, but we were careful when moving it. I'm sure it would be a lot more difficult and risky with a big tank.

choff · Feb 26, 2014

Excellent thread and good timing for me. I want to convert my DSB to DSB. Looking for input on the best way to do this. I currently have 1/2" to an inch of Carib sea special grade and picked up a couple hundred pounds of Tropic Eden reef flakes and mini reef flakes. The tank is 150G DT (rsm 650) running close to 2 years.

Thanks

choff · Feb 26, 2014

Won't let me edit... That should be SSB to a DSB in case you couldn't figure that out....

FlyinBryan · Feb 26, 2014

2.5" in DT but a 7" dsb in the fuge. It's going great.

jgraz · Feb 26, 2014

jgraz said:
I have learned tones from this thread. I just put a DSB in a 65gal tank that will serve as a refugium also. This is of course going to te attached to a 200+gal system as it comes along. I kept it seperate so that I could avoid messing around. I did however start with dry sand. I will seed this with some of the sand from my 90 when I break it down. That tank has about a 2.5" bed, so is it still worth seeding from it. I put out a call to local reefers but all seem reluctant to give me a bit of sand. I really want this DSB to be everything it possible can. So I ask you all what are the best creatures I can add? When should I add them, Ive heard that I sould wait awhile for the worm pack from indo pacific. And beside IPSF.com where can i find the stuff I need.

Thank you all, and please keep up this discussion.
John

Anyone have any opinions on the questions I posed here. Could really use some.

Mike J. · Feb 26, 2014

Your existing sand would be a great addition; scoop it off the top 1/2". A live rock will have a lot of the critters you'll want. Why wouldn't someone give you some sand? I would if you were closer. Also, I'm a big believer in live sand; every time I started a tank with it I've had clams hatch and lots of other critters.

TriggerThis · Feb 27, 2014

Wow lots of risks being taken.
You can move around a DSB all you want but your gonna cause die off and it can take a very long time to build back up enough of the right bacteria in the bottom for there to be an impact on nitrates.
The sand has to be fine enough to make a low oxygen area. You have to use the sugar fine sand and no more than 5". After 5 there's no oxygen and there will be only death down there causing all that area to turn black. Then if it's disturbed it will crash the tank with toxins.
If you move a DSB that's working correctly you will cause die off and possibly hydrogen pockets that can crash your tank.

Eienna · Feb 27, 2014

It's not the easiest read - you may have to skip some parts - but here's a scientific article on hydrogen sulfide as it applies to reef tanks.
http://www.reefkeeping.com/issues/2005-12/rhf/index.php

Mike J. · Feb 27, 2014

TriggerThis said:
Wow lots of risks being taken.
You can move around a DSB all you want but your gonna cause die off and it can take a very long time to build back up enough of the right bacteria in the bottom for there to be an impact on nitrates.
The sand has to be fine enough to make a low oxygen area. You have to use the sugar fine sand and no more than 5". After 5 there's no oxygen and there will be only death down there causing all that area to turn black. Then if it's disturbed it will crash the tank with toxins.
If you move a DSB that's working correctly you will cause die off and possibly hydrogen pockets that can crash your tank.

Where did this information come from? Have you personally witnessed such catastrophic events with a DSB? "No more than 5". "After 5 there's no oxygen and there will be only death down there..." This information is far from factual. It's actually wildly exaggerated and should be the subject of a fictional horror story.

The recommended depth of a DSB is 6" - 12". It is actually a rare occurrence that a DSB becomes toxic enough to hurt our animals. The tank would smell to high heaven before it reached the dooms day toxicity you're projecting. The anaerobic bacteria that thrives in low oxygen areas of the sand bed is the whole purpose of a DSB - it uses nitrates as a carbon source because of a lack of oxygen and converts nitrates to harmless nitrogen gas.

There have been studies done that confirm that hydrogen sulfide is present in the ocean. There also have been studies done that show it takes a high amount of hydrogen sulfide to kill our pets. A higher level (and smell) than your wife or husband would put up with. Once a myth gets started it's really difficult to quell it.

The truth is that a sand bed between 1/2 inch and 3 inches is usually not deep enough to reduce nitrate and yet too deep to be fully aerobic. In other words, it will collect nitrates but not consume them and will become a "nutrient sink". I have personally dealt with tanks with these not deep enough depths of sand and they are a maintenance nightmare.