re:substrate question

>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 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!

Take about a teaspoonful of your gravel, put it in a glass, and cover it with 
about 1/2" of vinegar.  If it fizzes, your gravel has calcium carbonate in it.  
If your gravel has calcium carbonate, it will buffer your pH upwards, even 
against CO2 injection.  

I'll leave it to someone else to explain the evil chemistry involved, but most 
aquarium gravel contains carbonates, and carbonates tend to buffer the pH to 
the alkaline side.

I usually use quartz blasting sand for my tanks to keep the substrate out of 
the chemical equation for the tank.

David W. Webb
Enterprise Computing Provisioning
Texas Instruments Inc. Dallas, TX USA
(214) 575-3443 (voice)  MSGID:       DAWB
(214) 575-4853 (fax)    Internet:    dwebb at ti_com
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