Metals in fresh water tanks?

I need to know if galvanized steel with zinc in it is ok to put in
fresh water tanks with fish and plants in them? The reason why I need
to know is that I am occasionally using a vortex diatomaceous filter
(xl model) and I only have had success by using hose clamps made out of
the previously mentioned metals. The hoses do not securely hold the
sponge prefilter which keeps my babies from getting vacuumed out of the
tank and into an unknowing death in the filter, unnoticed (at least
until it is too late). I am convinced that the previous mentioned
metals would be dangerous in a salt water tank, wreaking havok in it.

Could someone recommend a particular anti-parasite medication that
won't harm the biological filter or plants, which I might have a use
for in the distant future? Later, thanks.