Betta Fish: How often should I change the water w/ this many plants?

I've had this planted tank growing/cycling for nearly 2 years. Today we got my gf the fish she's been wanting for ages. Seems healthy + active and is already eating. How often should I change the water w/ this many plants sucking up the waste? Plants are java fern, anubias petite, moss balls, and a big pothos vine growing out the top. Fishy close-up at the end 🙂