Re:Possible substrate problem

     >My fish and plants don't seem to mind being at 7.5 (they're used to 
     >it by now).  It's easy to keep hard-water cichlids in Austin 
     >tapwater, but I'd like to evolve my tank into a community river tank.
     >My concern is that I won't be able to introduce new fish and more 
     >difficult plants. I was trying to lower the pH with CO2, but at the 
     >current KH, there's no way to get to pH 6.9 without making Fish-Cola.
     First, I want to congratulate you for reading the Krib and the 
     archives BEFORE you posted a question here.  I am extremely weary of 
     people posting their problems here, when the question has already been 
     answered.  Thank you.
     Austin water comes from the Colorado River, which has a hardness of 
     120 ppm CaCO3 and pH 7.5.  Sound familiar?  It's no wonder your 
     aquarium will equilibrate to 7.5.  It's not your substrate; there is 
     no need to tear down your tank.  BTW, you already have a community 
     river tank!
     Of course your fish and plants don't mind a pH of 7.5--there is 
     absolutely nothing wrong with 7.5!  You mentioned your plants were 
     doing great.  Haven't you noticed the lush growth of native aquatic 
     plants in the Colorado River and Barton Creek?  I suspect you have 
     been listening to some of the aquarium shops here--they love to sell 
     unnecessary water conditioners (even phosphate-based pH adjusters!) 
     and often over-exaggerate the hardness of the water here.  They know 
     not.  Ignore them.
     I keep a 30 gallon plastic trash can full of tap water.  I aerate it 
     for 48 hours, and voila!  The chlorine is gone, pH is stable, and no 
     additives were necessary.  I draw all my changing water from here.
     From my experience, you have several choices.  You can leave you tank 
     as-is, and do quite well.  The aquarium shops here also use Austin 
     water, so the fish you buy will already be acclimated.  Plus, these 
     fish come from a wholesaler in San Antonio, which has very similar 
     water.  Vallisneria, Ludwigia, Hygrophila and Hornwort do very well 
     here.  The San Marcos River is a great place to collect these plants.
     However, if you want to grow Amazon swords or Apons or anything that 
     is moderately difficult, you will need to consider some kind of 
     substrate additive (laterite, loamy topsoil, etc).  Since you have 
     already read the Krib, you know what I am talking about.  I use 4" of 
     loamy topsoil/vermiculite overlain with 1" of sandblasting gravel.  I 
     got the topsoil from Wolfe Nursery--40# for $0.99.
     You will also need to add CO2--10-15 ppm CO2 will result in a pH of 
     about 6.8.  This equates to about 2 bubbles/second from a CO2 
     generator.  I use a 20# tank with a regulator and needle valve, 
     purchased locally.
     You will also need to add fertilizer-I use PMDD, and it works great.  
     I regularly sell my excess plants back to the aquarium shops; you may 
     have purchased some of mine!
     In summary, you don't have a problem.  You can leave your tank as is 
     and to very well, or you can make some modifications and do 
     exceedingly well.  Whatever you do, don't listen to any of the 
     aquarium shops!  The APD and Krib is your best source for good advice.