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Re:Malachite Green - no copper

I don't suppose ths will put the issue to rest, but...

I tested my favorite Malachite Green solution, "Ich Cure" from Aquatrol at
the normal dose, 10 times the normal dose and 100 times the normal dose on
our Hach pocket colorimeter and got 0.00 ppm, 0.00 ppm and -0.08 ppm copper
respectively (I'm assuming the huge dose of malachite green in the last test
finally made the sample blue enoughto confuse the electronic eye).

I then called Bill Goodwin at Aquatrol and, after he was done chuckling, he
verified that Ich Cure contained no copper.  He also explained that part of
this misconception might come from the fact that metals (most commonly zinc)
were sometimes added to malachite green dyes to help them bond to clothing
(it's common commercial use), and that some early fish books cautioned to be
sure that malachite green used in aquariums be free of metals.  To the best
of his knowledge, no manufacturer adds copper to their malachite green.

On the practical side, I routinely treat several hundred aquariums with Ich
Cure, most of which contain aquatic plants.  I have yet to see any plants
appear to suffer from the treatment, with the possible exception that new
Crypt. balansae melt down about half the time after I add the Ich Cure. (On
the other hand, new balansae seem to melt down about half the time for me

Three other things leap to mind about  malachite green:

First, it will stain the sealer in the seams of all glass aquariums.
Whether or not it's worth this nuisance is of course in the eye of the beholder.

Second, I've noticed malachite green to be much more toxic (to fish, at
least) in very softened well water (pH 7.5-8.0, GH 0, KH 10+).  I'm not sure
what part of this combination causes the problems, but the only "overdose"
situations I've seen over the years all appear to occur in this sort of water.

Third, I've had equal success curing "Ich" using half doses 12 hours apart
instead of the recommended full dose every 24 hours.  Even sensitive fish,
like tiny tetras and pictus cats, seem to tolerate this level, so this may
be an even safer method for planted tanks as well.