Deep Sand Bed Experiences
looking for peoples experiences concerning the Deep Sand Bed.
problems i've heard presented are nutrient buildup and fears of Hydrogen Sulfide.
i'm aware of those concerns.
internet and forum searches for info and possible problems have reached a dead end culminating in the above mentioned concerns about why they are not a good thing to use in an aquarium (any aquarium - freshwater and saltwater)
waiting for the new year when finances are again available (welcome to Christmas expenses)
asking ahead of time so i can get an idea what problems to expect and what can be done to resolve those issues.
curiosities i've got
-sand grain size ?
-sand depth ?
-how long it's been running (how long before it failed) ?
-any spikes in ammonia/nitrate/nitrite ?
-(for those that failed) guesses, observations, symptoms, smells going on when it failed, even those that don't seem relevant ?
-any critters in the substrate (if present/used) ?
everything i've encountered about why a deep sand bed should not be done are given the same argument: concerns about Hydrogen Sulfide.
i'm aware of how toxic this gas is in the aquarium. it's one concern. a concern that, as much as i can find, can be neutralized. a concern that has been brought up by people who do not talk about what they were using in their substrate (above questions)
Subbing in here, as this is a question I also have. My tank has a fairly deep sandbed toward the back, and I've been watching things closely - but this tank has only been set up since September. I had a similar setup in a smaller tank for a year previously with no problems. . . Tahitian Moon sand is what I'm using, though it's a bit of a coarser grained sand than many, I imagine the same issues still would crop up.
I have a rather large rock on one end that I assume is where problems would occur if any should, but I do my best to poke under it every few months with a hairpick, I'm not sure if that's enough, lol! I also have added MTS to this tank, and it's fairly well planted. My hope is that the roots from the sword plants will find their way underneath the rocks and 'fix' any problems that might occur.
Anyway, let me know if you find anything concrete, and a *BUMP* for those who know more to stumble across this thread! :)
Small grain size (playsand)
been running 3-4 months before failure
whole room smelt like rotten eggs for 2 days, no spikes, one plant had rotted, silicone stained yellow in one spot, huge gas bubbles under decor and in sand, no deaths.
No snails in the sand
Been running at least 6 months without failure
No spikes, no critters in the sand, the one time I rearranged no gas bubbles under decor or anywhere at all.
Only difference was that the 15 gallon I would stir the sand and in the 20 gallon I do not. Food for thought...
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I'm glad you mentioned that, Lympie. . .I've always wondered - because stirring the sandbed kind of allows mulm and other wastes to become trapped under the sand and become the start of a problem. . . yeah. Food for thought, for sure!
You should not stir up a SW sand bed. If its a Reef tank, you can stir up the likelyhood of killing alot of things releasing alot of trapped waste at one time.
heehee, I apologize! I didn't realize I was looking in the SW section *bangs head* Whoops!
what i have learned in the last month about DSBs
a DSB is ... a bit of a conundrum.
it starts off doing what it's supposed to do, providing an anoxic environment for anaerobic bacteria to complete the nitrogen cycle.
as the DSB ages the hypoxic substrate tends to grow (gotta look into this more, i think it's related to CO2, but that's somewhat a guess) and the anoxic substrate slowly oxidizes till there is no place left for the anaerobic bacteria to complete the nitrogen cycle (i've heard initial theories where a deeper sand bed, ... things where considered 6-10" or more to solve this. this starts to get a little ridiculous about how much sand is in your tank when you bought a tank that's 24" deep and it's half full of sand. do not add sand directly ontop in any sizable quantity or you will kill everything you buried, including bacteria that are now starved for O2, ... creates an ammonia spike
add to this the default consideration for a reef tank, aragonite, (calcium carbonate) binds with phosphates. not the intention of the DSB, but one of those unplanned side-effects with unplanned consequences. as phosphates bind with the substrate the differences are how deep a substrate just changes how long before all the aragonite sand is saturated in phosphate bonds.
unfortunately, what we think is chemically bound to the the substrate is also PH dependent. and bacteria in the substrate tend to create their own environment independent of the water column. and these little mini environments are localized in sections of the sand bed (not the whole thing). as the PH in these little mini-environments changes, it changes everything. if the PH drops the phosphates are then released into surrounding environment, which is aragonite saturated in phosphates. so these phosphates move directly to the water column. this says nothing about bacteria acting directly on the detritus and phosphates in the substrate.
a deeper sand bed prolongs this as the phosphates that are released when the mini-environments do their thing ... those released phosphates have somewhere to go.
the phosphate issue is independent of the anoxic issue.
sand beds also collect detritus, this is either allowed to site undisturbed till it fills the sand bed up, or it's vacuumed out. if it's left to sit, it's up to you to decide if that's good or bad, over the years, that's a lot of detritus. if you want to vacuum the sand your mixing your sand layers exposing high oxygen water to the deeper sand which is meant to be an anaerobic environment to complete the nitrogen cycle that processes nitrate into N2. killing this bacteria that cannot survive in a high O2 environment
i've explored ideas of adding vascular plants to the tank to deal with nutrient buildup, vascular roots add O2 to the substrate, undoing the whole purpose of a DSB.
in the end a DSB is nothing more than someone who has put in 3" or more of sand (regardless of the type of sand) in the bottom of the tank
if you pick a sand that is not calcium carbonate based that will be rather inert, then just omit the bonding process and the same stuff happens regardless. based entirely on bacterial activities though. there is no initial phosphate reduction due to calcium carbonate bonding, and later there is no surplus of phosphate released due to unbonding processes. just a gradual release from detritus due to bacterial activity
initially it will work to process nitrates into harmless N2, the kicker is so will Live rock
so i'd stick with a sand bed that serves your purposes either for asthetics, for plants, or for any critters in your tank that have specific requirements.
being 6" or 2", if it's providing denitrification qualities what does it matter how deep your sand bed is to be called a Deep Sand Bed
if it's beyond 6" and it's no longer providing denitrification for your tank, it's just a lot of sand. isn't the whole DSB philosophy based on providing an anaerobic environment in the substrate ? if it's done in 2" then i guess that's all that's needed. so if you've got 4", or 6" or 10" or more, ... not getting the point of denitrification, is just a lot of sand. what else is a DSB for ?
the hardest part of learning about DSBs was that no one was talking about them, i went months searching till i found a forum that openly talked about what is going on. usually they bring it to aspects of phosphates, often calling it "nutrients". then they mix the 2 and avoid what the DSB is about and focus on phosphate issues.
it's quite a search to find people talking about DSBs as a function of what DSBs are doing to themselves. one way or another, regardless of the depth, over time, the deeper levels slowly saturate with oxygen. which is going to defeat the purpose of a DSB as it needs it's lowest levels to be depleted of O2.
manually stiring the bed, if your getting a rotten egg smell, you've been releasing H2S into your water column. it's a very toxic gas better left at the bottom where it formed. in time H2S diffuses through the substrate to reach the water column on it's own. H2S is also very reactive, while it's diffusing upwords it has a chance to meet O2 and is neutralized before entering the water column. manually stiring your sandbed is releasing your H2S directly into the water column before it has a chance to be neutralized.
personaly i refer to this practice as intentionaly wanting to kill your fish, unless you have that goal in mind, please stop it. H2S is a gas and can be gassed off and out of your tank as well.
What happens in a deep sand bed (DSB) assuming it is working correctly is low oxygen bacteria are reducing nitrates to nitrItes then to nitrogen gas.
So at the surface oif the sand you have low oxygen, higher co2, nitrogen gas. Which is the exact environment for cyano bacteria which get their nitrogen from nitrogen gas vrs the algae using ammonia/nitrates.
Plus if not working correctly the DSB bacteria can further reduce the nitrItes to ammonia and return ammonia to the system. Obviously that would then feed the aerobic bacteria and is not a good thing.
So there are many reasons to not trust a DSB other then sulfides.
But that said some have ran DSBs for years and years.
To me consuming the nirates with algae is a much better situation because the algae also consumes phosphates and carbon dioxide and returns oxygen and fish food. Not to mention helping grow pods and stuff.
And if something goes bump in the night the algae prefers to consume any increased ammonia.
Just my thoughts.
worth .02 at most.
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