Toxic gas build-up in sand?

[flyinmike]

If it is too deep you can get toxic gas building up under the sand. When there's enough of it, it can bubble up through your tank and poison the water.

I've seen this happen in my 180 gallon tank. I put in 1.5" of sand initially, but the fish move it about and soon enough there were mountains and valleys. And after a while I spotted small bubbles coming from the mountains...

There's now a lot less sand in my tank. Fortunately I didn't lose any fish, but the sheer volume of gas I unearthed as I scooped out the sand was quite disturbing.

Curious, how did you know it was toxic?

I'm guessing it is hydrogen sulphide, it certainly smelled like it: rotten eggs. It can quickly bring down your pH. If your pH is already low, then H2S certainly won't help your fish....

That's where the discussion sits so far. Anybody else had this occur?
Also, I know that oxygen transfer takes place at the surface. The only thing air bubbles do is agitate the surface to create more transfer area. Is this not true with other gas as well? Wouldn't a ventilated top keep buildups from occuring? To me if you can smell it then it is not mixing with the water but rather escaping. Not to go on and on, but if there is the toxic gas getting in the water would not proper filtration and plants help to control it. I'll stop now so someone else can talk..

[JohnnyOscar]

My (basic) understanding is that the sand settles to form a "blanket" that blocks out gas transfer. You end up with anaerobic bacteria breaking down organic matter to produce Hydrogen Suphide.

You have a point about gas exchange and tank hoods. That had never occurred to me-- this tank does not yet have one.

Within 15 minutes of disturbing the "gas field" I had completed a 40% water change, so I guess my fish never got a pH shock.

I would also like to hear more about this. Good call mike

[Barbie]

I had this discussion at a cichlid forum a few months ago. The general consensus was that I was insane, the deeper substrate and anaerobic spots under them couldn't have off gassed enough sulfide gas to hurt my fish. The multipunctatus that I had in the tank would surely have disagreed with them, as they were quite stressed, but I didn't lose any.

The sand I was using was a fine silica pool filter sand. I had only put just over an inch in the tank, but the multis are tiny shell dwellers that shift their sand and shells around to create their personal ideal space. The deeper spots in the sand were carefully vacuumed and moved around with each weekly 30% water change (30 gallon long tank, with 6 tiny shell dwellers and 2 bristlenose as total bioload). The problem, as far as I could tell, is that the particulate size of the sand, didn't allow heavy vacuuming, or I'd remove the sand also, so despite stirring, and my attempts to vacuum well, the spots continued to get worse every week, until I finally removed about 3/4 of an inch worth of the sand. The fish were determined to get the sand away from their shells down to bare glass anyway.

If you looked at the bottom of the tank, from underneath, you could see very dark spots whereever the sand was too deep on the surface. I personally make sure I don't use fine sand substrates, and that its not more than 3/4 of an inch deep or so. That's plenty of substrate for the fish, and then there is no risk.

Who knows, maybe the problem I was having in the multi tank would never have killed them, but it DID make them act gaspy when I would disturb those pockets, and IMO, they were stressed, so I resolved the problem by removing part of the substrate. The black patches in the sand went away,and I had no more occurences of sulfide gasses burping from the substrate. Seemed like an easy solution to me.

Barbie

[flyinmike]

So Barb, what type of cover was on the tank?

[Barbie]

Glass lids, with an aquaclear filter on the back, definitely far from air tight

Barbie

[flyinmike]

Well, for the time being I'm going to leave my substrate as is but I will be keeping an eye on it.
I do wish some more people would chime in on this topic. This is my first sand tank and I very much like it and plan on setting up more, or converting over to, sand.

I had this discussion at a c*****d forum a few months ago.

Could you give the link to that so I (and others) may go and read that?

[Barbie]

http://cichlid-forum.com/phpBB/viewtopi ... highlight=

[Shane]

I think it is best to keep sand less than 1/2 inch in depth to avoid these problems. If you need deeper sand (for example, for certain fishes that bury themselves) just place your fingers in the tank before your weekly water change and "rake" the sand. This keeps it stirred up enough and also helps dislodge food particles and fish waste so they can be siphoned out.
-Shane

[Pectorale]

Shane wrote

place your fingers in the tank before your weekly water change and "rake" the sand

Make a habit of doing just that, my fish trail my fingers to snap up any leftover food particles or algaecrusts ( between sand and glass). Of course you could also add a real digger like Callichthys to your tank. It helps prevent problems like blue algae covering your sand.

[flyinmike]

On a different forum I read that malaysian trumpet snails will burrow through the sand and help reduce chances of gas buildup. I had some going in a different tank as loach "treats" so I dropped some in my 110 and they instantly started burrowing into the sand. I've dropped about 20 in there now and most of them are under the sand. We'll see ??

[Coryman]

flyinmike,

The next time you se them they will have multiplied 1,000 fold.

Ian

[flyinmike]

flyinmike,

The next time you se them they will have multiplied 1,000 fold.

Ian

Yes, I will have to drop a couple of clown loaches in there when they start to get numerous. I drop them in my 55 where there are two loaches and they love them.

[Hongi]

Just out of curiosity, why do people use the stars when they mention cichlids?

On some other sites I have seen people do this with Pleco, they always write Pl*co. What's up with that?

Oh, I guess the word cichlids is blocked.

[Stuey]

Hi there,

I must admit I was very anxious about using sand as a substrate to begin with. However, as I had a group of 10 wild caught sterbai and I wanted to try and persude them to spawn I went ahead, mainly as I had read fine sand is best to avoid damage to their barbels.

I found any food that was uneaten, settleds on the top, and could be siphoned on very easily. The corys managed to disturb enough of the sand to prevent any major dead spots.

It is true that the anaerobic metabolism of bacteria will produce hydrogen sulphide. This will cause damage to fish gills in particular, even at fairly low concentrations (something I have tested with collegues in the past on fish farms).

I use a thin plastic rod to poke around in any deeper bits of sand just to prevent any dead spots.

I have just used sand as a substrate in my 45 gallon tank, so I am hoping to avoid any.


I would be keen to learn of any other ways to prevent dead spots.

I guess heating cables in the substrate may cause enough current to prevent any, but I can not afford to test this at present

Stu

[Barbie]

Just don't make the substrate more than an inch deep and it won't ever be an issue, IME.

Barbie

[flyinmike]

Hello all! Loooong time no posts. I just wanted to drop in and update what I have experienced with the sand in my 110. I have been fortunate in that there has been no gas build-up under the sand. I believe the M T snails have been helpful with this. They burrow into the sand during the day and come out on the glass at night for some algae. Some one in the tank likes to munch on them so there has not been a population explosion. Some thing else that probably helps are the plants (which seem to love the sand) and the fact that everywhere there are no plants changes like sand dunes in the desert. Parts of the tank that were 4" deep are now only 1" while other parts that were 1 are now 4. This being due to current and an L-200 who almost seems to throw sand just for enjoyment (perhaps he's the great green snail hunter?)..