When to do water changes

[verochloeedgar]

Hi guys!
I have cycled my tank and now I am aiming to do water changes every 7 days but usually nitrates go over 20 by day 3 or 4. Can I keep it until nitrates reaches 40 or is this too bad?? I have a 20 galon tank with one plant and marimos and 2 small goldfish.
Thank you!

 

[dalto]

It depends on the fish but I never let it go above 20 if I can avoid it. As opposed to more frequent changes can you change more water each time? How much water are you changing?

 

[verochloeedgar]

I have been changing 69-70% every 3-4 days. I have added an extra plan today. I will keep that so it doesn't go too high. thank you very much!