Anaerobic substrate

[matubula]

I've noticed that parts of the gravel substrate (2-3mm) in my small tank have gone, what I presume is, anaerobic. When disturbed some bubbles are released and there is an unpleasant sulphur smell. The substrate is only a max of 1cm deep and interspersed with larger pebbles. The area that is affected is where the most pebbles are and the detritus collects.

I'm puzzled. The tank is about 60x40x30cm 70 litres, has 12 small Hypancistrus L066 about 7cm, is filtered by an Eheim 2215 external (spray bar) and Eheim Aquaball 180 (venturi). The temperature is about 28/29* celsius.

I tested the water before I did a 1/3 water change. Ammonia 0mgl, Nitrate 25mgl, pH 6, gH 5, kH 3. And I usually do two 1/3 water changes a week.

I haven't used a substrate for a few years now, so I'd be grateful for any advice.

 

[bigbird]

Hello Matt,

My theory, no scientific proof but my experience. The smaller the sand or gravel, the less chance of detritus getting to the lower part on the base. The larger the gravel, the more chance of airspace or detritus getting down to the lower parts of the base. IE Small gravel more compact, large gravel less compact. If you mix fine and large gravel, it can occur that after detritus settles in the large gravel and fish move around, they bury this detritus, thus trapping the gasses when the detritus decays. That is why we always state gravel vac the substrate. This does 2 things, aerates the soil and also sucks up the detritus. A few things to consider. 1 gravel vac more or change your substrate to fine silica sand and also maybe get some water movement in that area where the detritus collects. I only use silica sand as substrate and have my base at 1cm roughly and all my plants either floating, on logs or in pots. cheers jk :thumbup:

 

[Lornek8]

Sounds like your presumtions are correct. Unles you use an undergravel filter or something similar, filtration will do little to deter the formation of anaerobic zones. All you can do is be sure to stir/vac and or get some MTS.

 

[dw1305]

Hi all,
Matt, it does sound like it has gone anaerobic, it is only in the absence of oxygen that you get hydrogen sulphide production and the "eggy" smell

Sulfate-reducing bacteria (resp. sulfur-reducing bacteria) generate usable energy under low-oxygen conditions by using sulfates (resp. elemental sulfur) to oxidize organic compounds or hydrogen; this produces hydrogen sulfide as a waste product.

I'd also agree with both Bigbird and LorneK about causes and cures.

All you can do is be sure to stir/vac and or get some MTS.

cheers Darrel

 

[matubula]

I already disturb the substrate during WC but will do it more conscientiously. What is/are MTS? Does the anaerobic'ness affect the water negatively?

 

[Lornek8]

MTS = Malaysian Trumpet Snails

The anaerobic'ness creates a build-up of hydrogen sulphate/sulphite gas which is toxic, its what gives that pleasent rotten egg smell. Stale sections of substrate can also be a haven for bacteria. Many times a stale substrate, not necessarily from going anaerbic but from the conditions which lead to it, is a reason for "mystery" deaths of bottom dwellers. Mid & upper level swimmers may be unaffected but bottom dwellers get sick. Similar type conditions are often asssociated with fry & bare-bottom tanks not cleaned often enough.