i always stick to one rule when it comes to water perameters, stable is always better than spot on, obviously without going to extremes like if your water is ph8.5 when it comes out the tap. a lot of fish wont cope with that so it has to be lowered or stick to rift lake species.
fish can get real unhappy about changing water chems constantly.
the only real exceptions to that rule are discus, other very delicate species and african rift lake species.