I've had my 20 gallon trop tank running for about 3 years now and I'll admit, I don't test the water too often because it is such a well established tank.
Well...I tested it last week and the pH is 6.0....at the most, that's as low as my test kit goes. Out of the tap my water is about 6.8. I'm a bit concerned, I don't know if I should try to raise it or not. I have tetras and cories only in there and I know that the tetras at least like low pH. I did a waterchange and added a little kH buffer which also raises pH, but I don't know if I should do anything more drastic. As I've said, it's at the lower limit of my test kit so it may actually be below 6.0. Any ideas? I was planning on getting a few guppies or female bettas this week but I don't want ot have the poor things go into shock when I add them to my tank!

I wouldn't use chemicals to raise your pH. If you aren't careful, pH fluctuations are one of the hardest things for fish to endure. Even the chemicals say never more than .5 on the scale in whatever amount of time.

So I would keep doing water changes, maybe every four or five days, and really get down in the gravel and clean it out. Fill to the top with fresh water. You can keep using the kH buffer if you want, it'll keep the pH from fluctuating too much.

I don't know anything about caring for tropicals. I hope you get things ironed out though.

Thanks for the advice
I think the big, frequent water changes may be a good idea. That way I can bring the ph up to the same level as my tap water, but gradually. Luckily my fish all seem quite fine, but I'd be happier if it was a little higher.