Peat substrate and Lime Containing Rocks

I'm in the final phases of testing various substrate material and tank 
decorations before setting up a 135gal tank.  The peat and clay for my 
substrate cause the pH to lower.  Rocks I would like to use cause an 
increase and most importantly buffer my tank - KH w/o rock is 2, KH w/ rock 
is 3.  The peat/soil test tank is not dropping the pH as much as it did at 
the beginning of the test.  I do not know if this is because my Chinese 
Algae Eater is no longer digging up the gravel and exposing the peat (he got 
some buddies and is much happier) or if the peat is not leaching as much. 
 The 135gal tank will have the new Sandpoint substrate heating system so 
there will be a current in the substrate.  Therefore, I anticipate longer pH 
dropping potential.  Has anyone used peat in the substrate along with 
substrate heating?  If so, how long did the pH lowering effect continue?  My 
concern is that the peat will stop lowering pH long before the rock stops 
increasing it.
Rochelle Williams
williaro at ftmcphsn-emh1_army.mil