On Wed, 14 Jul 2004 13:56:52 +0200, "Ali Day"
wrote:

I have had guppies in a tank with a pH of 6.5 and soft water and they
seemed okay for about 2 months it was at this level. However some
platies I bought didn't survive at this pH and soon after I added
crushed coral to the tank to increase the pH and hardness, so don't
know if they'd have been happy in the long term.

As the other poster said if you have tetras they prefer a lower pH and
so altering the water chemistry probably isn't a good idea. Also if
you have plants they generally prefer water with a pH below 7 as it
has more CO2 in it.