More on vermiculite
> From: Stephen.Pushak at hcsd_hac.com (Stephen Pushak)
> Date: Wed, 7 Jun 95 12:57:44 PDT
> Subject: What happened to the list? + Vermiculite
> aquarium water? Vermiculite is a high CEC type of clay which is expanded
> to contain lots of air. When you put it in the substrate, you soak it in
> water and mince it up and then mix it with the lower layer of your
> substrate. Then you put a layer of gravel on top of that and add your
> aquarium water *carefully*. Vermiculite provides a similar function to
> laterite in that it provides lots of Cation Exchange sites (C.E. Capacity =
> CEC) where positively charged ions (cations) like NH3+ and phosphate ions
> will tend to be loosely bonded. There is an equilibrium that is reached
> that depends upon various ion concentrations, pH, temperature etc. Now the
> good thing is that these nutrients are now in a position where they can
> be absorbed (by cation exchange) by the microscopic plant rootlets! This
> is a wonderful thing because it means that they are NOT floating around
> in solution for the algaes to feast upon!! :-)
Perhaps a better solution is to use any of the smectite clays. They have
a CEC comparable to vermiculite but wont cause the floating problem. I
have a friend who is now experimenting with it (I've only got one plant
tank and I dont want to mess with it :) or I'd do the experimenting). The
smectite clays should probably be mixed at the same ratio as laterite (~
500g/ 50 tank). One problem may be having the clay suspended in the water
when the plants are uprooted but if you are careful this may be minimized.
> Now another idea springs to mind. What if we were to fill a cloth bag
> with a few handfuls of vermiculite (dirt cheap from that garden place :-)
> and just measure nitrates and phosphates before and after heaving the
> bag into a test tank. Whaddya think?
This should work but it seems that it might take a lot of vermiculite to
filter the water, the CEC is about 150 meq/100 g. I also think it will
preferentially adsorb things like iron before monovalent ions.
> I can't try it because I've got a pretty good tank going with lotsa plants
> and I'm not eager to create an algae garden in the tank with my new
> Lace plants. (shucks :-) So my nitrates are pretty low and I don't have
> a phosphate test kit.
I love to experiment. but not on my nice plant tank either!!!
> I hope this stirs up a nice controversial discussion on the relative merits
> of laterite vs. vermiculite. I know there's another side to the story but
> I'll just wait. :-)
I'm not convinced that CEC is the only or most important variable to
consider when using a substrate additive. I do think that by mixing a
good fertilizer with a high CEC material when creating a substrate can
be beneficial. Dupla provides a tablet to mix with their laterite
when first placed in the tank and perhaps this has the same effect.
This CEC conversation is very interesting I just wish we had some proof
of its impact. Perhaps further "testing" by hobbyists will narrow down
its significance in plant growth.