How often should I be changing the wather?

[MagickFish]

How often should I change the wather of my Aquarium? And how mutch should I change?

[Severus]

What size tank and what kind of fish do you have in it. For example of you have a messy fish like an Oscar or something the water changes will need to be heavier/ more frequent

[William]

100gw is right. The amount of fish, species of fish and aquarium size is very important in this equation, However if you want a rule of thumb for a normal working not overstocked community aquarium I would say about 15-20% once a week.

[Severus]

Like William said, as a general rule of thumb i think 20% once a week would be sufficient for most tanks