when to do water changes

my tank is fully cycled and heavily planted so there’s only ever trace amounts of nitrates in the water. online everywhere it says to do it when nitrates get up but I barely have any of them lol… i’m not looking for a “one a week” type answer, more of a what would happen in the tank for it to need the water change. my coolers make the water evaporate like crazy too so I have just been adding around 3 gallons of treated water every 2-3 days.

please do not come and yell at me and say that my tank isn’t cycled because of lack of nitrates, it is cycled.