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Re: Substrate question

Matt Van Buskirk wrote:
> I am currently suffering substrate problems.  I have come to find out 
> after planting 50+ plants in my 135 gallon tank that my $20 a bag gravel (which I spent 
> spent nearly 100 bucks total) is causing my pH to raise to 7.6 and 
> stay there.  Even my co2 tank is doing little to lower it.  What evil 
> chemistry principal is at work here, and how do I combat it.  I seem 
> to believe my only option is to remove my $100 dollar investment and 
> pave my driveway with it!

Is this the calcerous rock used for marine systems?  Lots
of crushed coral?  I understand that many marine aquarists
prefere this type of substrate because it helps keep the
pH high, at least for a while (buffers up to maybe 8.1, but
higher is even better for marine and the rock doesn't really
help at those levels).

However, marine aquarists find that algae, bacteria, or other 
sediment deposits essentially seal off the surfaces of the rock 
after a time (I don't know how long, but depends on aging and
detritus load in your system), and this buffering capability is 
largely lost as the system matures.  Marine aquarists talk 
about removing and treating the substrate with various acids 
to remove the accumulated coating and regain the buffering 
potential, but I guess you wouldn't care about that.  :-)

My guess:  Yes, it will always raise your pH.  While with
age and time the surfaces will get coated and sealed, you
are starting with a _much_ lower desired pH (like 6.8-7.0)
that this substrate will probably always impact, at least
marginally.  That means it should slightly increase your
hardness too.  In marine systems, since the pH is so very
high (like 8.5), the buffering potential is largely
lost with not very much time (and is not a big deal like
it is for your freshwater system).

Sorry about your gravel investment.  It's perfect for
a marine system, though.

--charley                           Fort Collins, Colorado USA
charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu