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Re: aluminum sulfate

On Mon, 23 Aug 1999, Michael Moncur wrote:

> A possible data point in favor of Al sulfate: Mardel's "Brite N' Clear", a
> product that claims to clear cloudiness and remove phosphates from aquarium
> water, lists Aluminum sulfate as its active ingredient. It also "has a
> softening effect on the water" according to the label.
> Does anyone think this may actually remove phosphates? I wouldn't add it to
> my aquarium, but I've been considering trying it as a pre-treat for
> changing water.

When the aluminum sulfate hits the aquarium water probably what will
happen is that the aluminum will react with the water to precipitate
aluminum hydroxide, leaving hydrogen ion and sulfate (= sulfuric acid) in
the water.

If it removes phosphate, then it's because the phosphate has a tendency to
adorb onto the precipitating aluminum hydroxide.  I don't think the
aluminum sulfate will have any effect on general hardness; maybe something
else in there does.  The hydrogen ion produced when the aluminum sulfate
hits the water will reduce the buffering capacity, and that could be what
they refer to as a "softening effect".

If your pH is lower than usual or if you add too much then you might get
enough aluminum staying in solution to cause problems.  If you're
interested in this sort of effect then you might be able to get it by
adding an acidified solution of ferrous sulfate or adding ferrous sulfate
granules directly.  The iron oxidizes and precipitates and phosphates go
with it.  The effect on alkalinity would be about the same as with
aluminum hydroxide, but the leftover iron isn't toxic - at least not in
small doses.

Nurseries sell ferrous sulfate under the name "cuperous" (or is it

Roger Miller