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Re: Dead Daphnia

> Leng Yee wrote:
> >
> > Hi! George,
> >
> > Thanks for the reply :-)
> >
> > I've siphoned off the dead ones and did a water change as you've mentioned.
> > I'll be getting the yeast as per your advice.
> >
> > I've one more question: how often should I change the water, if need be?
Hi, Leng Yee:
I hope that the water change helps. In any case, it can do no harm!
I seldom, if ever CHANGE the water. My practice is to harvest the
Daphnia by siphoning the water and replacing it. That way the chore of
changing water is replaced by a step that pays off in fish-food!
For replacement water I use about 25% of aged tap water (mine has about
400 ppm hardness, pH 7.1 and is from a well, (thus NO chlorine, which is
very toxic to Daphnia) and 75% of used aquarium water (hardness about
150 ppm), but I am not "religious" about the proportions.
The well water is aged for a day or two, to dissipate the oversaturation
of nitrogen. Oversaturation of nitrogen might, or might not harm the
critters, but I play it safe. Besides, once you have set up two
water-aging containers, its no chore. I use the same stood-up well
water, mixed with softened water, for the fish.
It pays to save the used aquarium water from fish-tank water changes -
it is definitely good for most life forms - let the gunk settle out and
use it for Daphnia culture. (The water from the Daphnia culture I use to
culture Tubifex worms; the water from the Tubifex ......  :-)
Daphnia (at least D. pulex and D. magna, in my experience) like
biologically tempered water from a fish tank. They thrive in it.
Ceriodaphnia (C. dubia) on the other hand, do not care for it. The fresh
water I add to supply any possibly exhausted minerals.
Really, you do not have to go to all that trouble just to culture
Daphnia! Good water and a little bit of yeast is all they ask for to
reproduce, & reproduce, & reproduce.
Siphon at least 50% of the water weekly (or about 10%, if you want to
harvest daily) because, in most cases, after about 3-4 weeks the Daphnia
stop reproducing. I thing that it is due to the buid-up of metabolites
(the so-called "Hemmungsstoffe"). A water replacement dilutes them. When
you replace the water, it is best to do it SLOWLY! I let it drip
overnight. Using this method, I have not had a single population crash
in the last 15 years!