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Re: Plant substrate [?] mystery

Matthew Mason wrote:

> Need help here. I have an aquarium friend with a peculiar problem.  After a
> 20% water change has been done on two of her tanks with plants, everything
> dies.  The water changes are every two weeks and the gravel is vaccumed in
> the process.  Here are the details:

So, what do the plants have to do with this?

"Everything dies" including the plants, or just the fish?  How big is the
fish load she's maintaining?

> 120g/40g (breeder)
> white silica sand substrate, 1 inch thick

Substrate appears to be a rather small part of these setups.

> low current/filtration

Low is a problem.  Probably high would fix the problem.

> shell dwellers and other cichlids

I suppose then that this should be taken to a "shell dwellers and other
cichlids" mailing list.

> plants

Cacti?  Sequoia?  Nightshade?

> 12/24 hours after sand vaccum
>         the fish are seen at the surface gasping for air (possible O2 depletion)

Low O2 or gill damage.

>         bloom

Bloom of what?  Is this where the plants come in?

>         surface scum/film
> pH 7.6
> Amm/Nitrite 0
> Nitrate 20ppm
> no chloramines
> What causes the fish to die?

Probably poor aquarium maintenance.

> Several possibilities:
>         Activation of dormant, good bacteria that remove all of the O2

Possible if she's pushing reasonable population limits and/or overfeeding.
Breaking up existing colonies can disperse the bacteria and temporarily
increase their activity. What distinguishes "good" bacteria from the other
guys, anyway?  Little white hats?

>         Anaerobic bacteria are stirred up and deplete the O2 somehow (not
> sure about how this would    work)

Obligate anaerobes would probably die.  Facultative anaerobes would act
like "good guys".

>         Phosphates (level not known) somehow fit in the picture

Not much information to go on, and certainly nothing about plants.  I'd
guess your friend is either supporting too many fish or over feeding the
fish she has and that allows a big bacterial population in the
substrate.  Cleaning breaks up that population and hordes of "free"
bacteria go on a rampage, using most of the available oxygen.  Later the
bacteria die back or settle to the substrate again, leaving things about
where they started.

More circulation might help through the crisis, but it doesn't solve the
original problem.

How long have these tanks been set up?  This doesn't sound like a problem
you'd find in a mature tank setup. Is your friend an experienced aquarium
keeper, or is this all pretty new to her?  Could there be toxic
contaminants in the makeup water (chlorine, chloramine, metals) that might
damage the fish's gills?

Roger Miller