Danios: Behaviour and appearance questions

Mean_Chlorine wrote:
Thusly Elaine T Spake Unto All:


You've got me curious because I've not seen pH stabilize around 7.5 when
I fill a tank calcium carbonate. I've always had hard, high pH
tapwater, though. When I stuff a tank with carbonates, it's usually for
marine fish or Tanganyikan cichlids and with hard water to start with,
the pH generally ends up above 8.0. If you have time to elaborate on
the equilibrium chemistry for soft water or have a link, I'd enjoy
taking a look.


If you start with very hard water, it'll take very long for the acids
and CO2 produced by your fish & plants to drive pH down to where the
limestone will start reacting; quite possibly it'll never happen if
you top up with hard water or do regular water changes - the buffering
capacity of the water itself is such that the buffering capacity of
the limestone never comes in to play.

That is, you start with so hard water that it doesn't matter what
rocks you put in. If you start with very soft water, you'll tend to
end up around 7.5.

Very hard natural water will at equilibrium have a pH of 8.3. This is
the highest pH you can get with bicarbonate (the product of limestone
dissolution and chief buffering component of natural waters).
Natural waters with a pH significantly higher than that (e.g.
Tanganyika, with a pH of 9 - 9.2) get that pH either because 'soda'
(hydroxide) is leaching into the water from the surrounding sediments,
or because there is so heavy plant growth that bicarbonate becomes
depleted (the CO2 content of the water is not at equilibrium with the
atmosphere).

Also, and don't take this the wrong way, but unless you're using a
recently calibrated electronic pH meter, ie you use
drip-titration-kits or, worse, pH paper or multisticks, you don't
actually know your pH with greater accuracy than +/- 0.5 to 1 unit,
regardless of what it says on the box.

Thanks - that makes sense. Basically you're saying that bicarbonate
from calcium carbonate only reaches its 8.3 pKa in natural waters where
the amount of limestone is huge and the water has years of slow contact,
right?

I mostly use liquid bromthymol or bromphenol blue for measuring pH
around neutral. I'm not sure what the indicator is for my liquid high
range kit. However, you reminded me of the classic science lab
experiment where you put a drop of BTB in distilled water. Gently blow
on it for a bit and it goes yellow. Shake hard for a little while and
it goes blue. Similarly, it's wickedly hard to get a reproducible pH
measurement on a CO2 injected plant tank with a liquid kit.

I actualy don't have too much trouble with my liqid kits getting
reproducible measurements within a given day in my hardwater non-CO2
tanks (I've tried this), but you're correct that I don't know the accuracy.

--
Elaine T __
http://eethomp.com/fish.html '__
rec.aquaria.* FAQ http://faq.thekrib.com

On the coloration of your Zebras... the males have a silver tone to
them while females have a golden tone between the black lines. You will
notice as they get larger, the females will become increasingly
aggressive towards the males and they will become more gold in color
and very wide. Sometimes they can be double the size of the males. A
larger group will cut down on the aggression.

On your leopards, there is a gold variety, a regular variety and a blue
variety. There is also a long finned variety, just like in Zebras. If
your fish are more gold then silver, you probably have gold leopard
danios.

Leopards (brachydanio frankei) and Zebras (brachydanio rerio) are two
different species, so they will not breed. Although, I am sure there
are hybrids; they will be more likely to breed with their own species
first. Golden zebra danios, long finned golden zebras, long finned
zebras, and short finned zebras, can all breed together since they are
the same species... just different fancy strains created from specific
breeding. Same goes for the leopard color varieties and tails listed in
the second paragraph.

Thusly " Spake
Unto All:

Leopards (brachydanio frankei) and Zebras (brachydanio rerio) are two
different species, so they will not breed.

AFA is known that is not true. The leopard has never, despite
considerable effort, been found in nature, and is now believed to be a
captive-bred strain of zebra danio, and /Danio frankei/ is today
considered a synonym of /Danio rerio/, with which it will also
interbreed. However, the leopard danio has reduced fertility, which
*might* indicate that it itself is a hybrid between /D. rerio/ and
some other species of /Danio/.

The genus /Brachydanio/ is today considered a synonym of /Danio/,
comprising most of the small species of danios, whereas the genus
/Devario/ comprises most of the big species (e.g. /Devario
aequipinnatus/, the common giant danio).

Also, FWIW, I do not recall ever having seen a silver or blue strain
of leopard danio or zebra danio. I have seen albinos & partial
albinos, though.

Thusly Elaine T Spake Unto All:

Thanks - that makes sense. Basically you're saying that bicarbonate
from calcium carbonate only reaches its 8.3 pKa in natural waters where
the amount of limestone is huge and the water has years of slow contact,
right?

Pretty much, although in most cases you'll never actually reach 8.3.
Even in areas where the bedrock is limestone, natural surface waters
usually have a pH of 7.5 - 7.7-ish.

I actualy don't have too much trouble with my liqid kits getting
reproducible measurements within a given day in my hardwater non-CO2
tanks (I've tried this), but you're correct that I don't know the accuracy.

The liquid kits usually aren't bad, and for normal aquarium use you
don't need to know the pH with greater accuracy than 0.5 - 1 unit; pH
is simply not that critical unless you have a specialty aquarium (e.g.
high-tech plant tank or maintain a pH below 6 or above 9). The pH
papers and multisticks, however, are atrocious. Maybe they're OK when
they're fresh from the factory, but after a year or so on the shelf
they're usually so wildly off that one IME is better off without them.