Aquarium Disaster

[MichaelJ]

Thanks Michael, if I get the pH back up is that sufficient to control those traces or is the substrate which will be four years in the tank come August had its sa

I’m not entirely sure what I would advise. For sure, I wouldn’t want to be in a situation where a change in pH could cause loss of livestock - which never happens in a healthy tank unless the change is extreme. If it indeed was a release of toxins from the substrate then you would have to get rid of those toxins. If you still have livestock in the tank and increase the pH your high TAN level could be potentially lethal. If it would be me, and I couldn’t find another plausible reason such as illness, I would probably tear it down and rebuild the tank. You have several tanks so I’m sure you could temporarily house any remaining livestock.

Cheers,
Michael

 

[Serenade4]

Thanks Michael

I decided to move the remaining three fish out of the tank as I had space in the 200l. I started to get the rotton egg smell from the substrate so I have stripped the tank down and will start again.

 

[dw1305]

Hi all,

I started to get the rotton egg smell from the substrate so I have stripped the tank down and will start again.

That is hydrogen sulphide (H2S) and I'm guessing that that is where your issue lies. Not in hydrogen sulphide directly, but in what it <"indicates about the dissolved oxygen level in the tank">. The links in the linked thread will cover this area in more detail.

The two questions that I'd like to ask are:

• What <"was the substrate in the tank">? and
• What <"media do you have in your filter">?

cheers Darrel

 

[Serenade4]

Hi Darrel

The substrate, which is now in the bin, was JBL Sansibar with some lightweight gravel type stuff that my LFS sold me when I said I wanted to grow plants. I never added any soil, nutrients when I set the tank up.

Filter is the standard Fluval U3 with the standard media that comes with it.

 

[Scaperinc]

I would go for aquasoil if you plan to have rooted plants and you can cap that with sand if needed , I put crushed lava rocks under the aquasoil , only because I refuse to spend money on ADA substrate, which is probably the best but expensive, jbl products are not bad at all tbh.

 

[MichaelJ]

That is hydrogen sulphide (H2S) and I'm guessing that that is where your issue lies.

Yes I think you're right. Darrel, I always thought very dense and compact substrate would be more susceptible to this sort of problem - essentially that the substrate gets to be anaerobic due to the lack of oxygen and in turn gives room for the creation of toxic gaseous hydrogen sulphide. However, @Serenade4 's substrate doesn't appear to be very dense - although it appear there might be a bottom layer that is. My own belief is that flow within the substrate (i.e. decent grain size and good bottom layer flow) and lots of rooted plants will prevent this situation from occurring in the first place - especially as the tank ages.

Cheers,
Michael

 

[Serenade4]

When I was taking the old substrate out it did seem quick hard packed at the bottom of the tank. I used nutribase and gravel, topped with sand in my most recent tank so will do something similar on the 125l. Plants we to like that ok

 

[Andy Pierce]

That is hydrogen sulphide (H2S) and I'm guessing that that is where your issue lies. Not in hydrogen sulphide directly, but in what it <"indicates about the dissolved oxygen level in the tank">. The links in the linked thread will cover this area in more detail.

Hydrogen sulfide is toxic, so if the substrate was disturbed and released a lot of H2S in principle that could have contributed to the killing.

 

[dw1305]

Hi all,

Hydrogen sulfide is toxic,

Yes, point taken. I should have made clear that H2S is toxic.

so if the substrate was disturbed and released a lot of H2S in principle that could have contributed to the killing.

It would have done.

It would also have exposed areas with very low ORP values and a <"very large oxygen demand">. In waste water treatment adding hydrogen peroxide (H2O2) is often used to oxidise any H2S. You need to add about 1 - 3 mg / L H2O2 per 1 mg / L H2S. <"https://onlinelibrary.wiley.com/doi/full/10.2175/106143015X14362865225951">*

* If the link stops working the reference is Chan & Farahbakhsh (2015) "Oxygen Demand of Fresh and Stored Sulfide Solutions and Sulfide-Rich Constructed Wetland Effluent" Water Environment Research 87.8 721-726.
cheers Darrel

 

[Serenade4]

So does all substrate have a finite life in a tank? Would vacuuming help (although I always thought that would remove nutrients and disturbing it might cause HS to be released)?

 

[dw1305]

Hi all,

So does all substrate have a finite life in a tank?

It would probably depend on how <"physically stable it is">. I use silica sand and potentially that remains "good" eternally.

Would vacuuming help

I'm not a vacuum fan, but it would be difficult with fairly fine sand any way. This is what Dr Stephan Tanner says: <"Aquarium Biofiltration - SWISSTROPICALS">.

might cause HS to be released

I'm still at a loss for why you add hydrogen sulphide (H2S) formation in your substrate. I don't know if @Andy Pierce has any idea?

I used to work with wastewater and it is something you experience quite often with grossly organically polluted water, but <"not usually in planted tanks">.

You need to get to values below about -50 milli V (<"oxidative reductive potential (ORP)">) for sulphate (SO4--) to become the electron acceptor and for H2S to form.

cheers Darrel

 

[Andy Pierce]

I'm still at a loss for why you add hydrogen sulphide (H2S) formation in your substrate. I don't know if @Andy Pierce has any idea?

The way I read this @Serenade4 has concerns that H2S is forming naturally in anoxic zones of the substrate.

 

[dw1305]

Hi all,

H2S is forming naturally in anoxic zones of the substrate.

I think that is the only explanation, what I'm not sure about is why are conditions amenable to H2S formation? There doesn't seem to be the input of nutrients that might provide a substrate and then reduce oxygen levels low enough to produce ORP values at a level for sulphide formation.

If you had a substrate with, say, <"green waste compost"> in it? I could understand it.

cheers Darrel

 

[MichaelJ]

Hi all,

I think that is the only explanation, what I'm not sure about is why are conditions amenable to H2S formation? There doesn't seem to be the input of nutrients that might provide a substrate and then reduce oxygen levels low enough to produce ORP values at a level for sulphide formation.

If you had a substrate with, say, <"green waste compost"> in it? I could understand it.

cheers Darrel

Yes, it definitely raises the questions about long term risks of compact soil/substrate. I would suspect it might take a fairly long time (perhaps years?) for enough organic waste etc. to accumulate deep in the substrate with reduced oxygen levels and in turn enough H2S formation before it becomes a ticking time bomb .

In nature it appears to be a common phenomenon in compact sediments.

Sulfide Concentrations in Sediments and Water and Their Effects on hard Clams - Florida Shellfish Aquaculture Online Resource Guide

Purpose: The hard clam Mercenaria mercenaria is a common inhabitant of estuarine sediments and an important aquaculture species in the U.S. In coastal environments, high nutrient inputs lead to increased rates of phytoplankton production followed by increased organic material availability...

shellfish.ifas.ufl.edu

Cheers,
Michael