Gases under the sand

[Young Frankenstein]

When I redid my tank I also changed the sand around. Now I see gas in my DSB when using a turkey blaster to clean some spots. What are these gases doing and when will they stop?

[seapug]

Most people will freak and think they are hydrogen sulfide, but they are probably just oxygen bubbles produced/trapped by algal films in the illuminated parts of the sand. If they were hydrogen sulfide you'd smell rotten eggs and probably see dead fish.

I get them from time to time as well. Usually in proportion to the amount of food put in the tank. I use the baster to turn the surface of the sand and they get set free.

[kirkbjerk]

Is it good to turn the sand from the onset of a new established tank so they never build up? Or does this defeat the purpose of a DSB?

[Young Frankenstein]

No theres no bad smell so I assume they are oxygen probably?

[bertoni]

They are likely oxygen or nitrogen gas. Turning the sand is likely to kill the animals that make the DSB live, so I'd avoid that. Personally, I'd ignore the bubbles for the moment, but watch for signs of diatoms, cyanobacteria, etc, which might be blooming.

[Young Frankenstein]

What gas you should have under a DSB ?

[bertoni]

There likely will be some hydrogen sulfide and hopefully some nitrogen. A bit of oxygen at the top layer isn't all that uncommon.

[Young Frankenstein]

ok what does having hydrogen sulfide tells me ? and I guess thats the rotten egg smell. what does nitrogen tels me and how can you tell you have nitrogen ? also how can you tell if is oxygen and what that indicates ?please explain

[seapug]

This is my understanding of this topic:

Hydrogen sulfide is created by anaerobic conditions. The idea is that anaerobic bacteria convert this toxic substance into harmless nitrogen. It occurs in oxygen deprived areas like Deep Sand Beds and inside live rock-- it's fuel for the "denitrification" process-- the main idea behind using live rock for natural filtration. If you cut live rock open, you'll smell rotten eggs. It's good that it happens there, but you do not want it escaping into your water column.

The worry about stirring/disturbing deep sand beds is that you run the risk of releasing large amounts of toxic hydrogen sulfide into the water column. It's more of a concern for very deep sand beds of sugar fine sand (like over 6") because it can only occcur in areas that are completely oxygen deprived. It's generally something people are overly paranoid in terms of stirring the sand in a tank with a 2-3 inch sandbed of course sand, because a turkey baster rarely disturbs more than the top inch or two where aerobic processes are taking place that create the algae films/oxygen bubbles you are seeing. From everything I've read and experienced, gently stirring or turning this top layer will not cause problems and can actually be beneficial by breaking binding films and releasing detritus that can clog the sand pores where beneficial aerobic bacteria thrive.

By stirring the top layer of sand, you're basically manually performing the job that large numbers of sand sifting stars, fish, nassarius snails, and hermit crabs do in nature. Plus, it can do a lot to keep the tank looking clean and bright.

[Young Frankenstein]

So an indication that your DSB is doing good is the rotten egg smell ?

[seapug]

no, the DSB should keep that smell contained within its depths just like the rock does.

[Young Frankenstein]

What if theres worms in the sand? will they die, help the de nitrification or they wont do anything ?

[bertoni]

The worms help move water, nutrients, and oxgen into the sand. They are basically the lungs of the system. H2S is produced by anaerobic decay:

http://reefkeeping.com/issues/2005-12/rhf/index.php

The sulfur cycle is not tied to denitrification, at least not very directly, I think.

[Young Frankenstein]

Thanks bertoni. So so we call the DSB establishment a "sulfur cycle" ? and denitrification in a DSB happens with a nitrogen establishment? I did read that article and a couple of more in RC but I have very little knowledge about chemistry, and is hard for me to understand some of this stuff. My big question is whats in a DSB and what I should watch out for basically. seapug answered some of my questions but I can say I am still a little confused.

[HPD Turbo]

<a href=showthread.php?s=&postid=9956777#post9956777 target=_blank>Originally posted</a> by bertoni
They are likely oxygen or nitrogen gas. Turning the sand is likely to kill the animals that make the DSB live, so I'd avoid that. Personally, I'd ignore the bubbles for the moment, but watch for signs of diatoms, cyanobacteria, etc, which might be blooming.

How can I tell diatoms, cyanobacteria??

[bertoni]

There are both sulfur and nitrate reactions in a DSB.

A microscope is need to identify diatoms and cyanobacteria.