What do the readings say in your tank? I noticed with my water, it comes out about 8.2 out of the tap, but once it sits for about a day or so (depending on if I'm testing water that's been sitting in a cup or in a gallon jug I've noticed it can vary), it goes down to 7... So you might want to see if the pH stays the same or lowers on its own before considering using something like pH Down. My water does that and what I do is I use gallon jugs and pre-treat the water and let them sit until my next water change (which is about a week). If anything, keep in mind bettas are pretty hardy- from what I remember, they can adjust and do just fine in a pH of 8.2, so it's nothing you should really worry about ^.^ Although, if I'm wrong, I would like for another member to correct me on this >.>;
I'm not really sure about pH Down, but from the vast majority of what I've come across- it's overall not the greatest of things to use in a tank. I believe what happens is it has the possibility of fluctuating in some way- and if it spikes or crashes too dramatically, it can kill your fish... Not quite something you should quote on me either, as I've never had that problem so I never really dug into it.... but hopefully I've recalled this information somewhat accurately, and I hope this helps you.
Last edited by Draug Isilme; 01-12-2012 at 08:25 AM.