BLEACHING POWDER COMPOSITION

Sent: December 29, 1999

From: Raúl Coyula <coyula@fbio.oc.uh.cu>
To: <Artemia-l@sparklist.com>

QUESTION:

Could anybody give me the chemical composition of "bleach" or "bleaching powder 70%" used for killing Artemia predators in solar saltworks?

***************

COMMENTS:

Formula = Ca(OCl)2. The 70% refers to the amount of active Ocl product (by weight) present. Normally this should be mentioned on the packet when you buy it. Take into account also that this amount goes down with time (especially if you store the powder in humid conditions).
To be absolutely sure, you can do a titration with thiosulfate using a KI
indicator (procedure can be found in any chemical handbook). Once you know the amount present, you can calculate how much bleaching powder you need (we usually recommend 10mg/l).
First applying urea at 15mg/l (to reduce the pH) increases the efficiency of the bleaching powder.
However, if the primary production in your ponds is high = if lots of
algae/organic matter is present, lots of the chlorine is lost in a
reaction with these products and you will have to use higher dosages.
Finally, this method is mainly effective if you have a way to concentrate predators in certain areas (often fish concentrate around the gates, where you eventually could install traps).

Peter Baert
House 3, Campus I
Can Tho University
Can Tho - Vietnam
Tel. : +/84/71/83.83.01
Fax : +/84/71/83.03.23

E-mail: bpeter@hcm.vnn.vn

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