Old Rock Wool - Potential Toxin

[Tonyb111111]

I was having a fairly good clean of the tank today and turning over the substrate quite deep, when I I unearthed some old rock wool from previous plants that have died. I notice that the sand is black around the wool and it can be you can smell it emanating from the waters surface, which is obviously decomposition. My question is what toxins are released into the water when you do this?

 

[ainsy]

I don't think that your rockwool is necessarily the cause - any sand bed can get these stagnant areas over time.

Best to give them a gentle stir every once in a while to prevent it happening.

Not sure what you have released but a range of water tests and a large water change is probably in order.

HTH

 

[KkAaNnEe]

Just have a search of anaerobic pockets, nothing to worry about, theres a lot of fuss about them but they are harmless, like ainsy said, your sand just needs a turn over now and again - its not the wool

 

[thereverendturtle]

If it smells like rotten eggs, its hydrogen sulfied gas. There has been debate as to weather or not its harmful to fish or not.

 

[Tonyb111111]

Thanks all, I usually turn the top cm or so of substrate but this time I went deeper as I noticed some old dead roots coming out of the sand. It is definitely hydrogen sulphide, which can kill humans as a gas in large enough quantity, but I do not know how it interatcts with water chemistry. There is lot of conflicting views out there so I will gauge it by my fishes behaviour, who look there normal selves this morning, and stats are fine.

I think I will do deeper substrate turns a bit of the tank at a time over a a few weeks to get rid of anymore that might be there

 

[Akasha72]

I recently bought plants grown in the rock wool stuff. It didn't feel right to add that to my tank so I spent some time pulling the plants apart from the wool. It was a messy job and left me with tiny bit of plant and bigger bits of plant but to be honest I felt it was worth it.
I didn't know if the rock wool would do anything to the water chemistry or harm my fish and I figured it probably was harmless (why else would they grow the plants in it?!) but I didn't want to find out in all honesty.

I'm glad I spent the time getting rid of it

 

[Tonyb111111]

I recently bought plants grown in the rock wool stuff. It didn't feel right to add that to my tank so I spent some time pulling the plants apart from the wool. It was a messy job and left me with tiny bit of plant and bigger bits of plant but to be honest I felt it was worth it.
I didn't know if the rock wool would do anything to the water chemistry or harm my fish and I figured it probably was harmless (why else would they grow the plants in it?!) but I didn't want to find out in all honesty.

I'm glad I spent the time getting rid of it

Like you, I take time to get the majority off before planting, but there is usually a bit left on. Its these little bits mixed with rotting roots that are the problem. Anyway, the fish seem fine, and that's all that matters.

 

[Akasha72]

Anyway, the fish seem fine, and that's all that matters.

It is indeed

 

[Primous]

A couple of things...

Rock wool will eventually disintegrate in all substrates including sand but crucially, you're only supposed to add 1cm of thickness to the substrate to anchor the plant not the whole thing. Anerobic areas which turn into hydrogen sulfied gas is potentially lethal. There is a lady on apc who detailed here near aquarium stock wipe out. Granted she has left the area untouched for some time (about a year if i remember correctly) but in short when it released, her fished were swimming on their sides within minutes because she didn't have adequate surface tension to mitigate the sulfied gas.

Though there is an easy solution to aerobic areas that require no work. From my understanding root growth will penetrate aerobic areas as they grow.

 

[Tonyb111111]

A couple of things...

Rock wool will eventually disintegrate in all substrates including sand but crucially, you're only supposed to add 1cm of thickness to the substrate to anchor the plant not the whole thing. Anerobic areas which turn into hydrogen sulfied gas is potentially lethal. There is a lady on apc who detailed here near aquarium stock wipe out. Granted she has left the area untouched for some time (about a year if i remember correctly) but in short when it released, her fished were swimming on their sides within minutes because she didn't have adequate surface tension to mitigate the sulfied gas.

Though there is an easy solution to aerobic areas that require no work. From my understanding root growth will penetrate aerobic areas as they grow.

Thanks for this Primous, does the root stock absorb nutrients from the anaerobic areas as they pass through and therefore get rid of them?

 

[KkAaNnEe]

I think it has something to do with the root system giving off oxygen, therefore not allowing the pockets to develop

 

[ian]

^^correct, the root systems will use the gases to thier advantages. I sit in the camp of 'these pockets cause no problems'.

a quote from Walstad

Diana Walstad in her book Ecology of the Planted Aquarium actually talks about the beneficial aspects of having anaerobic conditions under the substrate near the plant roots. She has around several inches of soil as the substrates in her tanks. The anaerobic bacteria will use most anything for an energy source, reducing nitrates is just one of them. The bacteria can also reduce iron, sulfur, manganese, and so on. The great thing for plants is that these reduced forms are much more easily taken up, so anaerobic conditions help the plants get their micronutrients.

If H2S hits 02 in the water it actually neutralises anyway. There is some equation for this kicking around somewhere. I know low tech tanks that have gone 2-3 years without having substrates touched.

 

[Juggler75]

From memory I believe H2S + O2 results in H2O + S, so basically water and Sulpher. How toxic is sulpher? Must depend on the ammount because remember its the smell we recognise when we add Prime.

 

[Tonyb111111]

Cheers Ianho, my scientific brain likes that explanation. So in a nutshell, leave the deep substrate alone and let the plants do there thing. The corys turn the top layers over anyway

From memory I believe H2S + O2 results in H2O + S, so basically water and Sulpher. How toxic is sulpher? Must depend on the ammount because remember its the smell we recognise when we add Prime.

Sounds right to me, and the sulphur will be mostly gaseous and leach to atmosphere through the water column I guess, with a few creating new compounds in the substrate possibly

 

[Juggler75]

It appears the balanced equation is 2H2S + 3O2 --> 2SO2 + 2H2O so 2 molecules of water and 2 of sulpher dioxide. Sulpher Dioxide is constituent of acidic rain since it mixes with water so readily. I'd ask again on the scientific forum where a chemist may help further.

It sounds scary but I'd guess any acids produced would be very diluted and therefore not dangerous. Might even help achieve the desired pH values.
My substrate is cat litter (fullers earth) topped with a fair bit of playsand which I stopped stirring very quickly as it led to the cat litter ending up on top in clumps. Haven't stirred in a good few months and although I can see small patches of black at the front, I also haven't lost any fish at all and my pH seems stable.