I actually wrote Seachem about the topic. Yes, they have a vested interest, but I think they have valid points:
We consulted with our chemist in regard to your email and
this was his response:
"First, I should tell you that Flourish Excel is not a 1.7
per cent glutaraldehyde solution.
Second, the "-cide" portion of the name "Metracide"
indicates it kills living organisms. That is why Metracide
is sold in the first place. If it were sold as an additive
for aquariums, I'm sure that the strength would be
adjusted to achieve the desired goal of enhancing plant
growth. As it is, it has the strength to kill microbes.
This means that it should be diluted, and carefully.
(Glutaraldehyde does real damage to the eyes, so I would
wear safety goggles.)
Remember that glutaraldehyde is a reducing agent. The
activator that comes with Metracide sounds like an agent
to increase the reducing ability of the glutaraldehyde. I
would most certainly avoid that. But it makes me wonder if
there is something other than water in the inactive
ingredients list, perhaps a buffer to help the activator
As a general rule, it is a good idea to wear gloves, and
to make sure that glutaraldehyde doesn't come in contact
with skin. Some chemicals are sensitizers, meaning that
repeated exposure to the chemical can cause a person to
break out in a rash, or worse. Glutaraldehyde is such a
chemical. I copied this from the OSHA (Department of
"Long-term (chronic) effects: Glutaraldehyde is a
sensitizer. This means some workers will become very
sensitive to glutaraldehyde and have strong reactions if
they are exposed to even small amounts. Workers may get
sudden asthma attacks with difficult breathing, wheezing,
coughing, and tightness in the chest. Prolonged exposure
can cause a skin allergy and chronic eczema, and
afterwards, exposure to small amounts produces severe
itching and skin rashes. It has been implicated as a
possible cause of occupational asthma."
The stronger the solution of glutaraldehyde, the greater
the chance of acquiring a chemical sensitivity. For the
record, somewhere in my 35 years of working in the
chemical industry I picked up a sensitivity to
glutaraldehyde. I also use Flourish Excel in both my
planted tanks, with no adverse reaction.
To play it safe, I would recommend continuing to use
Flourish Excel, and not substituting something that was
designed to do something other than deliver organic carbon
to plants. Of course, I work for Seachem, so you would
expect me to say that. But we develop our products with
the hobbyist, and not the hospital, in mind. Flourish
Excel is safe when used according to directions. It does
not have to be diluted. You don't have to worry about
developing chemical sensitivities. We do recommend that
you keep it out of your eyes, a good recommendation for
all our products."
I hope this information was helpful and please let us know
if you have any additional questions. Have a wonderful
Seachem Support 100215