Ammonia is more toxic in alkaline water.  As the pH drops below 7.0, toxic ammonia NH3 begins to convert to less toxic ammonia NH4++ . So a higher pH can be more dangerous, however....Biological filtration fails when pH drops below 6.4.  When this happens, ammonia builds up. Fortunately, since the ph is low it is less toxic.  This is dangerous because a sudden upward shift in pH, such as from a long overdue water change, will convert the ammonia into highly toxic ammonia!!! That is why regular water changes are so important and checking your pH before a water change is so important too.

Very good answer Minde!

No geez, never RE ADJUST pH but what I meant to try and keep it about 7.2 or neutral.
As I realized on this forum ther are pH s around 7.8 etc as Goldfish can take a wider range of pH. I always mentioned it is stressful if pH goes up and down like a Yoyo. This is to be avoided.

With this thread I only want to explain that it is better to have a pH neutral to 7.2. This is another reason I use ph neutralizer blocks.

Of course this should NEVER replace the regular waterchanges

It's the same with other nitrogens in the tank actually! The pH usually drops when the nitrites/nitrates get higher (I have experienced the same myself once :C). Which is why it usually decreases slightly during the nights while the plants aren't using as much nitrate. It's pretty funny how everything hangs together c:

Yes very interesting, I agree.  We have built an eco system in our fishes tanks and we are in charge of maintaining it to sustain life!