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Re: Iodised salt.

> Date: Tue, 25 Jul 2000 10:01:28 +1000
> From: "Neil Travis" <travisn at gravity_net.au>
> Subject: Iodised salt.
> Iodine is not added to table salt because people need it but purely to make
> it flow better as normal cooking salt which has is not iodised tends to mix
> freely with water and as such would clog up the salt shaker etc. and goes
> hard with moisture from the air as salt is hydroscopic. Iodised salt in high
> concentrations is poisonous to fish and should not be used in an aquarium
> only natural or non idodised salt is suitable.
> cheers

Sorry Neil, but almost none of this is true. It is ancient aquarium
mythology that I thought had died a natural death, years ago.

The salt is iodized to prevent goiter and other thyroid problems that
happened in humans where the water or diet didn't have enough. It is totally
non-toxic, and is routinely used at hundreds of times the concentration in
table salt to treat fish thyroid problems. Iodine and chlorine are quite
poisonous to fish. Iodide and chloride are not.

The free-flowing ingredients in table salt are usually either sodium
ferrocyanide (labeled with the medieval name "Yellow Prussiate of Soda" to
avoid panic among the chemically illiterate) or silica gel (silicates). They
both stop the caking and clogging, but apparently only the sodium
ferrocyanide is fairly safe for fish. The silicates leave a cloudy
precipitate that can clog gills. *That* is what started the ancient myth,
that still appears in some aquarium books despite being discredited long

The safest advice for a newby is to avoid free-running table salt unless it
is clearly labeled as using sodium ferrocyanide (prussiate...). Rock salt,
pickling salt, most (but not all now) kosher salt, are readily available
substitutes that won't harm fish, as they are pure NaCl. Read the label.

The kind of aquarium salt intended for reef/ocean tanks is also not a good
idea in fresh water tanks. In soft water, it often is buffered up around
pH=9.4 or so, which can make the tiniest amount of ammonia quite lethal. It
is great for hatching Artemia, but usually not a good idea in fresh-water
tanks, IMHO.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

           To err is human. To blame someone else is politics.
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