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Re: Sodium thiosulfate
From: SCraig9087 at aol_com
Subject: More on Ammonia
> Many "cheap" aquarium products use large amounts of
> sodium thiosulphate to reduce PH thereby converting ammonia to ammonium.
SCraig you may have a little typo here. The cheap aquarium
products use sodium thiosulfate to neutralize chlorine, not
ammonia. Na thiosulfate has a neutral pH in a concentrated
solution (6.5-8.0), so I would expect a 10% or whatever conc. is
used is pretty much around 7. On top of that you only use a couple
drops per gallon. I make a 50% solution and use around
(sometimes) one drop/gallon. I read in Tropical Fish that fish could
live in a 10% solution, which I wouldn't recommend, but I believe it
was mainly stated to show the passiveness of this compund in an
I think most pH reducers sold are phosporic acid based, not
> Unfortunately, if your PH goes up the resident ammonium converts back to its
> lethal form. Tropical Science makes a product (Complete Care) which breaks
> the chloramine bond and then converts the released ammonia into ammonium
> di-basic which is not sensitive to changes in PH. I don't know about other
> products, but using straight sodium thiosulphate can be a problem.
I use it liberally, sometimes a splash between water changes. As a
chemist, I'm very concerned about most additives, and am
meticulous about my measuring, so that ought to tell you how
worried I am of the thiosulfate. It's the only thing I don't measure.
I looked all through my literatures at work and cannot find an
ammonia use for sodium thiosulfate, but here's the cool
mechanism for the chlorine conversion:
Na2S2O3+4Cl2+5H2O = 2NaHSO4+8HCl and NaS2O3+2HCl =
It's also an antidote to cyanide. I guess it's good for heartburn from
eating too much cyanide. Talk about heartburn....