Water acidifiers

I have recently received the following message, in reference to one of my
recent postings:

<I'm sure I should have understood this from all the stuff I've read on the
list and elsewhere, but what are the problems caused by silicates?  And, if
you don't mind, to what pH decreaser were you referring?  I use Seachem
Acid Buffer.  Is this bad?  If so, you would be doing a great service if
you explained in more detail "by popular demand" from private message(s).


Dirk >

The problem I referred to in my letter occurred more than a year ago. This
is what I remember, but if anyone is interested I can try to dig out more
from my aquarium notes.
I had (and still have) a 20 gal planted (mostly E. tenellus) tank , newly
set up, back then with no CO2 injection. My pH control method for the south
american cichlids I have there was Seachem Acid Buffer, which is advertised
as being phosphate-free. Using a Red Sea (I hope this is the correct name;
it was made in Israel) kit I consistently had elevated phosphate levels
(that was the beginning of a strenous war still ongoing). I thought their
source was tap water and fish food, but when I discovered the existance of
phosphate-removing resins (Phos-Zorb) and used them for the first time, I
observed an unexpected pH increase. 
Suspecting that the buffer might not have been as phosphate-free as claimed
by the manufacturer, I called both Seachem and Red Sea customer
representatives. The former stated the no phosphates are contained in the
buffer, but that some phosphate measurement kits cross-react with silicates,
and since the buffer does contain them, this could have been the reason for
the elevated readings I got. 
The importer of the Red Sea kits did not have much technical information
available, but stated that a cross-reaction was a possibility. Another call
to the manufacturer of Phos-Zorb confirmed that not only phosphates, but
also silicates are removed by this resin.
So, I thought the loop was closed: the buffer increased the silicates
content of the water, being read as phosphates by the kit. The resin removed
the silicate-based buffer, causing a pH increase.
Please note that this is an hypothesis made by a non-chemist. I also am not
in the position of judging the effects of silicates on algae and plants
growth. I think I have read that diatoms (which have a silica-based
skeleton) may become a problem. I did have some algal growth in that tank,
but it wasn't a big problem and the plants were doing faily well anyway.
However, being upset at the poorly informative label of the buffer, I
stopped using it and I switched to CO2 injection (and a better phosphate
levels kit for which at least there is a decent technical support).
I hope this will help others to have an interesting discussion.