Regular water changes are Very important. Not only will not changing your water regularly affect your fish's health, but also if algae begins to grow it will use from the oxygen in the water resulting in less oxygen being available for your fish. If you do not own an air stone ,which provides oxygen for your fish in the tank/jar, algae growth should be monitored closely.
Oh and the rate of algae growth depends on the amount of sunlight received. The greater the amount of sunlight received the faster the rate of algae growth. Although keep in mind your plant needs some sunlight.