Water changes - which is better??

I'm not sure which one is the best way to do water changes... personally I do 15-20% water changes once a week.

With goldies the more oftent he water is changed the better. They do a lot of pooping. Ideally 30-40% twice a week would be best or 50% once a week. The more often you do water changes the closer your change water will be to the tank water so in an emergency situation you don't have to worry about any crazy pH spikes etc...

I would suggest buying a nitrate test kit and doing water changes whent he nitrates get over 20ppm. After testing for a while you will be able to set a decent schedual without regular tests. Then just test evry so often to make sure the level of waste hasn't increased.

Here's how I had it explained to me...

In the wild these fish live in a constantly changing environment. The water is constantly changing in a river or stream and impurities are constantly being removed. As long as the change water has the same make-up and temperatures, you can't do too many water changes.