"She'll suddenly go crazy" worries me a little. If you take a gander at acidosis and alkalosis in Immediate Help for the first one and maybe Google Guppylog for the second one, you may see why.

Different fish have different comfortable ranges in pH. As a good general rule it doesn't pay to mess with them. But if the water gets too acid for a particular specues they get what is called "crazy man's disease" though it is really crazy fish's disease and they race around the tank, banging into things and even harming themselves. If the water gets too alkaline for the fish, much the same happens.

It is sort of like their wiring gets all corroded and shorts out (he said, unscientifically). Since many water sources (in the US anyway) are buffered by water departments to be in the upper 7s of pH (which is also comfortable for guppies), simply doing more water changes or (and I know I flog this too much) walking up the percentages of weekly/ biweekly water changes from 25% to 30% to 35% & 40% and 45% is beneficial. One the one hand we are getting rid of some of the fish wastes (healthy in its own right). Also those fish wastes, when breaking down biologically cause the water to swing in an acid direction. The other hand is that the water changes add buffers which hold the pH up. (The water people like that because then the old lead pipes don't dissolve, mess people up and create interesting law suites.)

So while urging water changes sound hopelessly simplistic, it does remove harmful things and adds useful and beneficial things. A forest pond may gradually exchange 90% of it's water with the water table, every day. So too, streams  especially draw a lot of their water from the water table and weather and thus are also profoundly changing the water, all of the time.